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1762S-S 


ELECTRK^ 
RAILA\  AY  ENGINEERING 


ELECTEIC 


KAIL  WAY  ENGINEERING 


BY 

C.  FRANCIS  HARDING,  E.  E. 

professor,  electrical  engineering;  director,  electrical  laboratories,  purdue 
universitt;  associate  American  institute  electrical  engineers;  asso- 
ciate  AMERICAN  electric  RAILWAY  ASSOCIATION ;   MEMBER  SOCIETY 
FOR  promotion   OF  ENGINEERING  EDUCATION 


McGRAW-HILL    BOOK   COMPANY 

239  WEST  39TH  STREET.  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1911 


Copyright,  1911 

BY 

McGraw-Hill  Book  Company 


Prhited  and  Eleclrolyped 

by  The  Maple  Press 

York.  Fa. 


PREFACE. 


To  students  in  technical  universities  who  wish  to  specialize 
in  the  subject  of  electrical  railway  engineering  and  to  those  who 
understand  the  fundamental  principles  of  electrical  engineering 
and  are  interested  in  their  application  to  electric  railway  practice 
it  is  hoped  that  this  book  may  be  of  value. 

While  it  is  planned  primarily  for  a  senior  elective  course  in  a 
technical  university,  it  does  not  involve  higher  mathematics 
and  should  therefore  be  easily  understood  by  the  undergraduate 
reader. 

The  volume  does  not  purport  to  present  any  great  amount  of 
new  material  nor  principles,  but  it  does  gather  in  convenient  form 
present  day  theory  and  practice  in  all  important  branches  of 
electric  railway  engineering. 

No  apology  is  deemed  necessary  for  the  frequent  quotations  from 
technical  papers  and  publications  in  engineering  periodicals,  for  it 
is  only  from  the  authorities  and  specialists  in  particular  phases  of 
the  profession  that  the  most  valuable  information  can  be  obtained, 
and  it  is  believed  that  a  thorough  and  unprejudiced  summary 
of  the  best  that  has  been  written  upon  the  various  aspects  of  the 
subject  will  be  most  welcome  when  thus  combined  into  a  single 
volume. 

The  author  wishes  to  express  his  appreciation  of  the  assistance 
of  Mr.  Emrick,  instructor  in  electrical  engineering  at  Purdue 
University,  in  preparing  illustrations  for  the  book  and  to  those 
students  who  by  thesis   investigations  have  added  to  its  value. 

LaFayette,  Ind.,  September,  191 1. 


^01359 


TABLE  OF  CONTENTS. 


PART  I. 

Principles  of  Train  Operation. 

I.  History  of  Electric  Traction 3 

II.  Traffic  Studies  (predetermined) 13 

III.  Traffic  Studies  (existing) 24 

IV.  Train  Schedules 30 

V.  Motor  Characteristics      35 

VL  Speed  Time  Curves  (components) 48 

VII.  Speed  Time  Curves  (theory) 59 

VIII.  Distance,  Current  and  Power  Time  Curves  (theory) 66 

IX.  Speed,  Distance,  Current,  and  Power  Curves  (concrete  examples) .  71 

X.  Speed  Time  Curves-  (straight  line) 78 

PART  II. 

Power  Generation  and  Distribution. 

I.  Sub-station  and  Power  Station  Load  Curves 87 

II.  Distribution  System 91 

III.  Substation  Location  and  Design 104 

IV.  Transmission  System 131 

V.  Power  House  Location  and  Design       145 

VI.  Bonds  and  Bonding 170 

VII.  Electrolysis 178 

VTII.  Signal  and  Dis])atching  Systems 188 

PART  III. 

Equipment. 

I.  Track.  Layout  and  Construction 205 

II.  Rolling  Stock 219 

III.  Motors 232 

IV.  Types  of  Control      246 

V.  Brakes 259 

VI.  Car  House  Design 277 

VII.  Electric  Locomotives 288 

vii 


Viii  TABLE    OF    CONTENTS. 

PART  IV. 

Types  of  Systems. 

1.  Alternating  Current  vs.  Direct  Current  Traction 305 

II.  Electric  Traction  on  Trunk  Lines 319 


PART  1. 

PRINCIPLES  OF  TRAIN  OPERATION. 


CHAPTER  I. 

History  of  Electric  Tr.\ction. 

Although  it  is  not  the  purpose  of  this  treatise  to  relate  facts,  but 
rather  to  study  the  engineering  and  economic  problems  en- 
countered in  electric  traction,  yet  it  seems  advisable  to  re\dew 
briefly  the  history  of  the  development  of  the  electric  railway  by 
way  of  introduction. 

Two  distinct  epochs  were  encountered  in  the  brief  period  in 
which  electric  traction  has  come  to  the  front.  The  first  was  that 
in  which  the  experimental  designs  were  hardly  more  than  models 
operated  with  primary  batteries.  Occasionally  during  this 
period,  however,  enthusiasts  who  did  not  realize  the  insuperable 
financial  drawbacks  of  primary  battery  operation  constructed  and 
experimented  with  cars  of  considerable  size  operated  in  that 
manner.  Such  was  the  car  constructed  by  Page  in  1851  for  the 
Washington  and  Baltimore  Railroad,  which  made  use  of  a  16 
h.  p.  motor  supplied  with  power  from  two  large  Grove  cells  made 
up  of  platinum  plates  11  in.  square.  This  first  epoch  was  soon 
brought  to  a  close,  however,  partly  by  the  foresight  of  the  inves- 
tigators who  realized  the  limitations  of  the  primary  battery  and 
partly  by  the  failure  of  all  attempts  to  commercialize  the  primary 
battery  car  by  those  who  had  continued  to  experiment  therewith. 

The  second  epoch  opened,  after  a  brief  interval  of  inactivity, 
simultaneously  with  the  development  of  the  reversible  dynamo. 
In  the  development  of  this  machine  progressive  experimenters 
could  foresee  the  beginnings  of  electric  traction  upon  a  practical 
basis.  Bearing  in  mind  the  existence  of  these  two  periods,  the 
history  of  electric  traction  will  be  considered,  greatly  abstracted, 
but  as  nearly  as  possible  in  chronological  order. 

Since  electric  traction  has  ever  been  dependent  u})on  the  elec- 
tric motor  and  the  latter  upon  the  discovery  by  Faraday,  in  1821, 
that  electricity  could  be  made  to  produce  mechanical  motion, 
the  latter  date  rather  indirectly  and  vaguely  marks  the  birth  of 

3 


4  ELECTRIC    RAILWAY    ENGINEERING. 

the  subject  under  consideration.  America  has  the  honor  of  first 
applying  the  electric  motor  to  a  car,  model  though  it  was,  while 
later  developments  vibrated  from  America  to  Europe  and  back  to 
America  with  a  rapidity  difficult  to  follow  with  accuracy.  A  poor 
blacksmith  of  Brandon,  Vt.,  by  the  name  of  Thomas  Davenport 
has  the  honor  of  first  making  this  application  of  electric  motor  to  a 
car  in  1835,  the  motor  having  been  constructed  by  him  several 
years  previous.  During  the  short  period  of  six  years  it  is  said  that 
Davenport  constructed  over  a  hundred  electric  motors  of  various 
designs.  That  which  was  described  as  having  been  exhibited  by 
him  upon  a  car  at  Springfield  and  Boston,  Mass.,  consisted  of  a 
revohing  commutated  magnet  which  was  caused  to  attract  sta- 
tionary armatures  arranged  around  the  periphery  of  its  path  of 
revolution.  The  car  thus  equipped  was  operated  upon  a  small 
circular  track. 

About  the  year  1838  Robert  Davidson  of  Aberdeen,  Scotland, 
built  a  much  larger  motor  placed  upon  a  battery  car  16  ft.  by 

5  ft.  in  dimensions  of  the  gauge  then  standard  and  operated  same 
with  40  cells  of  battery  consisting  of  iron  and  amalgamated 
zinc  plates  immersed  in  dilute  sulphuric  acid.  It  is  of  interest 
to  note  that  after  several  successful  trips  over  Scotland  railways 
this  car  was  purposely  wrecked  by  steam  railway  engineers  who 
were  afraid  it  would  supersede  types  in  use  at  that  time. 

Two  rather  fundamental  patents  were  issued  in  England  about 
this  time,  one  in  1840  to  Henry  Pinkus  involving  the  use  of 
the  rails  for  current  conductors  and  another  in  1855  to  Swear 
which,  although  applied  to  telegraphic  communication  with 
moving  trains,  comprised  the  basis  of  the  present  current  collect- 
ing trolley.  Patents  were  also  granted  in  1855  by  both  France  and 
Austria  to  Major  Alexander  Bessolo  which  covered  the  same 
fundamental  principles  but  which  described  more  in  detail  the 
third  rail  conductor,  the  insulated  trolley,  and  even  suggested 
central  station  supply. 

The  experimental  work  in  this  country  of  Prof.  Moses  G. 
Farmer  in  1847  ^^'^  Thomas  Hall  in  1850  might  be  considered  in 
particular  because  of  the  use  for  the  first  time  of  the  rail  as  a  con- 
ductor and  the  adoption  of  a  geared  speed  reduction  between 
motors  and  dri\ing  axle.     The  work  of  Page,  previously  men- 


HISTORY    OF    KLECTRIC    TRACTION.  5 

tioned,  deserves  prominent  mention  at  this  time.  For  many 
years  after  these  experiments  investigations  in  electric  traction 
seemed  to  be  dormant,  largely  due  to  the  general  realization  of 
the  impracticability  of  the  battery  as  a  source  of  energy. 

The  second  era  of  electrical  railway  development  opened  about 
the  year  1861  when  Pacinotti  invented  the  reversible  continuous 
current  dynamo.  From  this  invention  may  be  said  to  have  arisen 
all  modern  generators  and  motors.  While  these  were  gradually 
developed  by  Gramme  and  Siemens,  Wheatstone  and  Varley. 
Farmer  and  Rowland,  Hefner-Alteneck  and  others,  Wheatstone 
and  Siemens  having  almost  simultaneously  developed  self- 
exciting  generators  equipped  with  shunt  and  series  winding, 
respectively,  yet  a  considerable  period  of  time  elapsed  before 
these  developments  were  effectively  applied  to  traction. 

The  work  of  George  F.  Green,  a  poor  mechanic  of  Kalamazoo, 
Mich.,  has  been  quoted  as  the  connecting  link  between  the  two 
eras.  Although  he  began  his  experiments  as  late  at  1875,  after 
the  development  of  the  dynamo,  his  first  model  road  reverted  to 
the  battery  delivering  current  to  the  car  over  the  operating  rails. 
Although  Green  proposed  the  trolley  for  his  experimental  track, 
he  did  not  make  use  of  it.  The  following  work  of  this  man  is 
rather  pathetic,  in  that  he  constructed  a  car  about  the  year  1878 
large  enough  for  two  people  and  realized  the  advantages  of  the 
dynamo  for  supplying  energy  for  same.  He  did  not  understand 
how  to  construct  this  machine  himself,  however,  and  was  not 
financially  able  to  procure  one  of  the  few  being  constructed 
abroad  at  that  time.  He  applied,  in  1879,  for  patents  which 
would  probably  have  been  of  considerable  value  at  that  time, 
but  because  of  limited  funds  and  the  fact  that  he  was  obliged  to 
act  as  his  own  patent  attorney,  his  claim  was  rejected  and  only 
fmally  granted  in  the  year  1891  after  a  belated  appeal  to  the  cir- 
cuit court  of  the  District  of  Columbia. 

The  first  electric  road  operating  on  a  practical  scale  was  the 
one  exhibited  by  Siemens  and  Halske  at  the  Berlin  Exposition  in 
1879.  This  consisted  of  an  oval  track  about  1/3  mile  in  length 
upon  which  an  electric  locomoti\e  was  operated  with  three 
small  trailers  accommodating  from  18  to  20  passengers.  The 
motor    was    mounted    with    its    axle    lengthwise  of  the  car  and 


^ 


i 


0  ELECTRIC    RAILWAY    ENGINEERING. 

power  was  transmitted  to  the  car  axle  through  a  double  bevel 
gear  speed  reduction.  A  speed  of  about  8  miles  per  hour  was 
attained.  The  current  was  supplied  by  means  of  a  third  rail 
located  between  the  running  rails. 

The  year  1880  in  Europe  marked  the  exhibition  of  another 
model  electric  railway  at  Vienna  by  Egger  which  used  the  running 
rails  for  conductors.  In  this  year  also  the  study  of  a  method  of 
replacing  the  pneumatic  dispatch  system  of  Paris  by  miniature 
electrically  propelled  carriages  was  carried  on.  Siemens  pro- 
posed at  this  time  a  commercial  road  for  Berlin  and  endeavored 
to  obtain  a  franchise  for  same. 

The  first  electric  road  to  be  installed  apart  from  an  exposition 
was  that  at  Lichterfelde,  near  Berlin,  which  was  opened  in  1881. 
A  single  motor  car  using  cable  drive  between  motors  and  axles 
operated  upon  this  road  which  was  i  i  /2  miles  in  length,  at  a 
speed  of  about  30  miles  per  hour.  It  was  sufficiently  large  to 
accomodate  36  passengers.  Although  a  third  rail  road  when 
installed,  it  was  changed  over  12  years  later  to  a  double  trolley 
system.  This  road  has  remained  in  continuous  operation. 
During  this  year,  also,  the  horse  railroad  between  Charlottenburg 
and  Spandau  was  changed  to  electric  traction. 

At  the  Paris  exposition  of  1881,  Siemens  and  Halske  demon- 
strated the  use  of  the  overhead  trolley  for  current  distribution 
to  cars,  the  conductors  consisting  of  metal  tubes  slotted  on  the 
underside,  mounted  upon  wooden  insulators;  in  which  tubes, 
metal  contactors,  electrically  connected  with  the  car,  were 
allowed  to  slide.  In  1883,  a  6-mile  third  rail  road  was  opened  at 
Portrush,  Ireland,  which  was  worthy  of  note  because  of  its 
operation  from  a  central  station  driven  by  water  power. 

Referring  back  to  this  country,  Thomas  Edison  and  Stephen 
D.  Field  began  experimenting  about  the  year  1880.  Edison  was 
principally  interested  in  the  development  of  the  incandescent  and 
arc  lamps  at  this  time  and  aside  from  building  a  short  road  at 
his  laboratory  at  Menlo  Park  and  taking  out  a  few  patents,  he  did 
little  in  this  line.  Field  did  considerable  pioneer  work,  having 
made  plans  in  1879  ^^^  ^  railway  to  be  supplied  with  power  by 
means  of  a  conductor  enclosed  in  a  conduit  and  using  the  rails 
as  a  return  circuit.     In   1880-81  he  constructed  and  put  into 


HISTORY    OF    ELFXTIRC    TRACTION.  7 

operation  an  experimental  electrical  locomotive  at  Stockbridgc, 
Mass.  Patents  were  applied  for  by  Field,  Siemens,  and  Edison 
within  3  months  of  each  other  early  in  1880.  Since  Field  had 
filed  a  caveat,  howe\'cr,  the  year  before,  his  pa])crs  were  given 
priority.  Field's  plans,  however,  remained  on  paper  until  the 
latter  part  of  the  year  1880  which  was  a  year  later  than  the 
installation  of  the  Berlin  road. 

Little  more  was  accomplished  in  the  United  States  until  1883, 
when  the  interests  of  Edison  and  Field  were  united  and  the 
Electric  Railway  Company  of  the  United  States  was  organized. 
This  company  exhibited  an  electric  Iocomoti^"e  at  the  Chicago 
Railway  Exposition  in  1883,  which  operated  on  a  track  about 
I  /3  mile  in  length  in  the  gallery  of  the  exposition  building. 
The  motor  operated  a  central  driving  shaft  by  means  of  bevel 
gears,  this  shaft  being  belted  to  one  of  the  axles.  The  speed  was 
varied  by  the  use  of  resistances.  Reverse  motion  was  accom- 
plished by  throwing  into  service  an  extra  set  of  brushes  by  means 
of  a  lever,  only  one  set  of  brushes,  of  course,  being  upon  the  com- 
mutator at  any  one  time. 

Charles  J.  \'an  Depoele,  a  Belgian  sculptor,  who  was  destined 
to  play  an  imj^ortant  part  in  the  later  development  of  electric 
traction,  entered  the  field  in  1882-83  when  he  operated  a  line  in 
connection  with  the  industrial  Exposition  at  Chicago.  After 
installing  ecj^uipments  at  the  New  Orleans  Exhibition  and  at 
Montgomery,  Ala.,  and  putting  roads  in  operation  at  Windsor, 
Ont.,  Detroit,  Mich.,  Appleton,  Wis.,  and  South  Bend,  Ind.,  the 
company  which  Van  Depoele  had  formed  was  absorbed  in  1888 
by  the  Thompson  Houston  Co.,  which  had  recently  been  organ- 
ized. The  name  of  Leo  Daft  was  one  that  cannot  be  neglected 
in  the  development  of  this  period,  for  after  considerable  work 
with  stationary  motors  in  1883  he  constructed  a  locomotive 
capable  of  hauling  a  full  sized  car.  The  control  in  this  car  was 
brought  about  by  varying  the  resistance  of  the  motor  field  for 
which  })urpose  some  of  the  coils  were  wound  with  iron  wire  in 
place  of  copper.  The  company  organized  by  Daft  at  Green- 
ville, N.  J.,  installed  roads  at  Coney  Island,  N.  Y.,  and  the 
Mechanic's  Fair  in  Boston,  and  in  1885  equipped  the  Baltimore 
Union   Passenger   Ry.    Co.   with   electric   locomotives.     During 


8  ELECTRIC    RAILWAY    ENGINEERING. 

this  year  electric  traction  was  applied  by  this  company  to  the 
Ninth  Avenue  lines  in  .New  York,  but  after  a  few  experimental 
runs  of  the  locomotive  termed  the  "Benjamin  Franklin"  the 
experiment  was  abandoned. 

In  1884  Bentley  and  Knight  installed  a  system  in  Cleveland, 
Ohio,  which  was  probably  the  first  to  come  into  active  competi- 
tion with  a  horse  car  line.  Two  miles  of  track  were  operated 
with  under  ground  conductor  in  wooden  slotted  conduit.  Motors 
were  connected  with  car  axles  through  the  agency  of  wire  cables. 

The  railroad  installed  in  Kansas  City,  Mo.,  in  1884,  by  J.  C. 
Henry  was  noteworthy  for  its  departure  from  other  designs  and 
its  adoption  of  features  which  have  since  become  standard  prac- 
tice in  electric  railroading.  Henry  claims  to  have  introduced  the 
use  of  the  overhead  trolley.  Whether  this  be  true  or  not,  the 
word  "trolley"  was  first  coined  by  the  employees  upon  this  road 
as  a  contraction  for  "troller"  the  word  first  applied  to  the  four 
wheeled  carriage  which  was  used  on  the  overhead  wire  as  a 
current  collector  and  connected  with  the  car  by  means  of  a  flexible 
cable.  The  use  of  the  trolley  rope  for  replacing  the  trolley  was 
of  much  more  significance  than  it  would  at  first  appear  because 
of  the  fact  that  it  was  formerly  customary  to  hire  a  boy  to  ride  on 
top  of  the  car  to  keep  the  trolley  on  the  wire.  The  present  system 
of  span  construction  and  feeder  installation  was  first  developed  by 
Henry  on  this  road.  His  overhead  conductors  consisted  of  two 
No.  I  B.  &  S.  bare  copper  wires  spliced  every  60  ft.,  for  this  was 
the  greatest  single  length  procurable  at  this  time.  The  rails 
used  were  those  which  had  been  installed  12  years  before  for 
horse  car  service  and  weighed  but  12  lb.  per  yard.  They  were 
at  first  bonded  by  dri\'ing  horse-shoe  nails  between  the  fish  plates 
and  the  rails.  The  motor  was  a  5  h.  p.  Van  Depoe  e  type  con- 
nected with  the  axles  by  means  of  a  clutch  and  a  five  speed  differ- 
ential gearing.  The  generator  was  a  series  arc  machine  of  10 
h.  p.  developing  a  voltage  up  to  1000  volts.  Although  Henry 
was  able  to  mount  7  per  cent,  grades  without  difficulty,  the 
Cleveland  road  was  the  only  other  practical  road  operating  in 
America  at  that  time  and  it  was  extremely  difficult  to  gain  the 
confidence  of  the  public. 

Of  the  roads  that  were  installed  during  the  next  few  years, 


HISTORY    OF    ELECTRIC    TRACTIOX.  9 

the  one  which  gave  the  greatest  impetus  to  electric  traction  and 
the  one  often  quoted  as  the  first  electric  road  in  the  United  States 
was  that  in  Richmond,  Va.,  equipped  in  the  year  1888  by  Frank 
J.  Sprague.  At  this  time  Mr.  Sprague  was  already  prominent 
in  the  railway  field,  although  much  of  his  time  had  been  given 
to  the  de\'elopment  of  the  stationary  motor.  In  a  paper  befoie 
the  Society  of  Arts  of  Boston  in  1885  he  had  advocated  the  equip- 
ment of  the  New  York  Elevated  Railway  with  motors  carried 
upon  the  trucks  of  the  regular  cars.  In  1886  a  series  of  tests 
were  carried  on  upon  the  tracks  of  the  34th  street  branch  of  this 
road.  These  experiments,  like  many  previous*ones,  however, 
were  finally  suspended  because  of  the  impossibility  of  interesting 
the  railway  management  sufSciently  to  launch  out  upon  a  com- 
mercial installation. 

The  motor  design  and  suspension  used  by  Sprague  in  these 
tests  were  the  forerunners  of  present  construction  and  therefore 
worthy  of  a  brief  description.  The  motor  frame  contained  bear- 
ings mounted  upon  the  car  axle,  thus  ])ermitting  the  former  to 
swing  slightly  about  the  axle  as  a  center  keeping  the  gear  and  pin- 
ion always  in  mesh  on  rough  track.  The  other  side  of  the  motor 
frame  was  hung  from  the  truck  frame  by  means  of  springs. 
Single  reduction  gearing  was  used.  Two  motors  were  used  on 
each  truck  but  they  were  open  to  the  weather.  The  first  designs 
were  shunt  wound  but  later  types  made  use  of  a  series  compen- 
sating winding.  Control  was  obtained  by  resistance  in  both 
armature  and  field  circuits.  The  motors  were  used  for  returning 
energy  to  the  line  as  well  as  for  braking. 

Before  considering  further  the  rather  important  installation 
at  Richmond,  it  is  well  to  consider  a  census  of  electric  traction 
develo]jment  early  in  1887.  In  Europe  at  this  time  there  were 
but  nine  installations  including  but  20  miles  of  track  taking  into 
consideration  every  type  of  electric  traction  including  thai  in 
mines.  In  the  United  States  there  were  10  such  installations 
involving  40  miles  of  track  and  50  motor  cars.  Public  prejudice 
had  not  been  overcome  and  no  system  of  any  size  had  been 
operated  commercially. 

The  Sprague  Electric  Railway  and  Motor  Company,  contracted 
for  installations  at  St.  Joseph,  Mo.,  and  Richmond,  Va.,  during 


lO  ELECTRIC    RAILWAY    ENGINEERING. 

the  year  1887,  the  latter  contract  covering  a  complete  new  road 
including  generating  station,  overhead  lines,  and  the  equipment 
of  40  motor  cars  with  two  7  i  /a  h.  p.  motors  each.  It  was  placed 
in  operation  in  February,  1888,  and  many  were  the  new  experiences 
and  amusing  anecdotes  connected  with  this  installation.  The 
distribution  system  consisted  of  an  overhead  conductor  mounted 
over  the  center  of  the  track  with  a  second  parallel  conductor  on 
the  pole  line  supplied  with  feeders  from  the  power  station  and 
extending  to  various  distributing  points.  The  power  station 
was  equipped  with  six  40  k.  w.  500  volt  Edison  generators  driven 
by  three  125  h.  p.  engines.  Upon  each  axle  of  the  car  was 
mounted  an  exposed  motor  in  the  manner  previously  described. 
The  single  reduction  gearing  employed  at  first  was  later  re- 
])laced  by  the  double  reduction  type.  The  speed  control  was 
effected  by  two  separate  switches,  one  changing  the  field  con- 
nections from  series  to  parallel  and  the  other  making  similar 
changes  in  the  armature  circuit.  The  cars  could  be  operated  in 
either  direction  from  either  end  and  the  entire  weight  of  the  car 
was  available  for  traction.  Motors  were  operated  in  both  direc- 
tions, at  first  with  laminated  brushes  fixed  at  an  angle  and  later 
with  radial  solid  metallic  brushes.'  The  success  of  this  road  at 
Richmond,  in  the  face  of  many  reverses  and  new  engineering 
problems  which  had  to  be  overcome,  was  probably  largely  due  to 
the  fact  that  Mr.  Sprague  was  the  first  man  with  a  competent 
education  to  enter  the  field.  With  this  technical  training  to- 
gether with  his  familiarity  with  the  failures  of  other  experiments 
and  the  development  of  the  stationary  motor  with  which  he  was 
closely  allied,  he  was  able  to  solve  the  many  difficult  problems 
which  arose  and  place  this  road  on  a  practical  operating  basis. 

From  this  date  electric  traction  became  firmly  seated  and  its 
future  development  was  rapid,  the  natural  tendency  being  to- 
ward hea\der  equipment.  After  investigation  of  the  Richmond 
system  the  West  End  Railway  of  Boston  soon  adopted  electric 
traction.  In  1890  the  South  London  road  was  equipped  with 
electric  locomotives  and  three  years  later  the  Liverpool  overhead 
electric  railway  was  put  in  operation.  Third  rail  trains  of  four 
motor  cars,  equipped  with  hand  control,  hauling  three  trail  care) 
were  used  at  the  Chicago  World's  Fair  in  1893  and  in  1896  the 


HISTORY    OF    ELECTRIC    TR.\CTIOX.  II 

Nantasket  branch  of  the  New  York  and  New  Haven  Railway 
was  electrified.  September  of  the  same  year  saw  the  Lake 
Street  Elevated  of  Chicago  begin  electrical  operations  and  two 
months  later  electric  service  was  begun  on  the  Brooklyn  Bridge. 
Since  it  is  impossible  to  further  list  the  new  electric  roads 
coming  into  existence  the  following  table  will  be  of  value  in  point- 
ing out  the  remarkable  growth  of  the  electric  railway  in  the 
United  States. 

TABLE  I. 
(Growth  of  Electric  Traction  ix  United  States. 

Year.  Xo.  electric  roads.  Miles  track. 


1889 

5° 

100 

1890 

200 

1200 

I89I 

275 

2250 

1894 

606 

7470 

1895  (July) 

880 

10863 

1902 

739 

22000 

Note. — The  decrease  in  the  number  of  companies  from  1895  to  1902  is  probably 
due  to  the  large  amount  of  consolidation  going  on  during  this  period. 

The  most  important  changes  in  motor  design  that  came  with 
this  progressive  movement  of  the  electric  railway  were  the  en- 
closing of  the  frame  to  protect  the  motor  from  the  weather,  the 
replacing  of  cast  iron  by  steel,  the  change  from  two  to  four  poles, 
the  use  of  form  wound  coils  and  carbon  brushes  and  the  return  to 
the  old  single  gear  reduction  between  motor  and  axle.  The 
control  system  of  1892  made  use  of  the  combined  resistance  and 
series  parallel  connection,  which  is  recognized  as  good  practice 
to-day  while  the  introduction  of  the  blow  out  magnet  was  a  long 
step  forward  in  controller  design. 

The  more  recent  developments  in  electric  traction  comj)ri6e 
the  use  of  alternating  current  for  transmission  to  substations, 
the  multiple  unit  control  of  the  various  cars  of  a  train  from  a 
single  master  controller,  the  use  of  alternating  current  motors 
on  the  car,  the  electrification  of  steam  roads  with  the  more  power- 
ful electric  locomotives,  and  the  use  of  high  voltage  direct  current 
system.     These  problems  are  of  such  a  broad  nature  and  so  im- 


12  ELECTRIC    ILVILWAY    ENGINEERING. 

portant  in  the  study  of  modern  practice  that  they  will  be  taken 
up  more  in  detail  elsewhere.  Suffice  it  to  say,  by  way  of 
historical  comment,  that  the  rapid  introduction  of  interurban 
railways  beginning  about  the  year  1894,  together  with  the  advances 
made  in  transformer  design  by  Stanley,  in  polyphase  transmission 
by  Ferraris  and  Tesla  and  in  the  synchronous  converter  by 
Bradley  and  others  brought  about  the  first  of  the  above  mentioned 
changes,  i.e.,  the  use  of  alternating  current  for  transmission  pur- 
poses. Probably  the  first  proposal  to  use  such  a  system  with 
substations  was  the  one  made  by  B.  J.  Arnold  in  1896  for  an 
interurban  road  to  run  out  of  Chicago.  Although  this  particular 
line  was  not  built,  a  similar  system  was  installed  about  two  years 
later.  The  multiple  unit  system  was  developed  by  F.  J.  Sprague 
who  proposed  its  application  to  the  New  York  Elevated  Railway 
in  1896.  After  several  vain  endeavors  to  secure  its  adoption  it 
was  finally  installed  the  following  year  by  the  South  Side  Elevated 
Railroad  of  Chicago  and  is  now  in  common  use  on  elevated  sys- 
tems and  is  used  to  some  extent  in  interurban  traction. 

Summarizing  briefly,  the  most  prominent  names  in  the  develop- 
ment of  the  electric  railway  are  found  to  be  those  of  Faraday, 
Davenport,  Farmer,  Hall,  Pacinotti,  Siemens,  Green,  Field,  Van 
Depoele,  Daft,  Bentley,  Knight,  Henry,  and  Sprague.  While 
gradual  developments  have  been  going  on  more  or  less  irregularly 
since  1835,  the  practical  electric  railroad,  operating  upon  a  com- 
mercial scale,  dates  back  to  about  the  year  1888.  \^ast  strides 
have  taken  place  since  that  date,  however,  until  at  the  present 
time  electric  traction  is  the  recognized  transportation  system  in 
practically  all  cities  and  towns.  It  has  tied  together  the  larger 
cities  with  facilities  for  rapid  passenger  transit  and  for  the  trans- 
portation of  both  express  and  freight.  It  has  opened  up  the  city 
markets  for  the  farmer  of  the  small  town,  and  the  country  sub- 
urbs for  the  residences  of  the  city  business  man.  It  has  com- 
peted successfully  with  the  steam  roads  on  interurban  lines;  it 
has  found  a  foot-hold  in  the  city  terminals  of  the  former,  and  is  at 
present  being  seriously  considered  and  in  some  particular  cases 
has  been  adopted  and  successfully  tried  out  for  trunk  line  ser\ice. 
Rightly  has  it  been  said  that  its  growth  is  without  a  parallel  in 
the  history  of  American  invention  and  industrial  progress. 


CHAPTER  II. 
Traffic  Studies  (Predetermined j. 

One  of  the  first  considerations  in  connection  with  the  planning 
of  a  new  railroad  or  of  an  extension  to  an  old  system,  whether 
it  be  within  the  limits  of  a  city  or  an  interurban  line,  is  the  study 
of  probable  traffic.  Upon  such  a  study  is  based  the  predeter- 
mination of  gross  income,  train  schedules,  and  power  station 
demand.  The  importance,  therefore,  of  an  accurate  and  de- 
tailed study  of  all  the  factors  which  may  affect  the  traffic  upon  a 
given  road  need  not  be  emphasized  further. 

Population. — A  study  of  the  railway  census  will  disclose  the 
fact  that  there  is  a  fairly  dependable  relation  between  passenger 
traffic  and  population  for  both  urban  and  interurban  railroads. 
In  the  latter  case,  of  course,  the  population  under  consideration 
must  be  that  of  the  two  terminal  cities  and,  in  most  cases,  a 
portion  of  the  intermediate  population  which  may  be  considered 
as  tributary  to  the  line.  The  determination  of  this  tributary 
population  is  rather  difficult,  being  largely  dependent  for  its 
accuracy  upon  the  experience  and  judgment  of  the  engineer.  In 
general,  however,  it  is  usually  taken  as  the  population  of  a 
strip  of  territory  from  i  12  to  2  miles  in  width  on  either 
side  of  the  proposed  railroad  and  parallel  thereto.  The  popu- 
lation of  such  a  strip  may  be  determined  by  actual  canvass  or  it 
may  be  assumed  that  the  township  or  county  through  which  the 
road  extends  is  evenly  populated  throughout  the  rural  districts. 
If  this  be  true,  the  tributary  population  may  be  found  from  the 
following  proportion. 

Tributary  population         Area  strip. 
Township  population     Area  township 

The  township  ])opulation  may  be  obtained  from  the  census 
reports  and  the  re<|uired  areas  scaled  from  a  map  of  the  territory 
in  question. 

While  it  will  l^e  found  ad\i>al)le  1m  make  an  analvsis  of  the 


14 


ELECTRIC    RAILWAY    ENGINEERING. 


relation  between  population  and  passenger  traffic  per  year, 
mileage  of  track  economically  operated,  gross  income,  etc.,  for 
the  entire  country,  a  table  or  series  of  curves  covering  such  data 
obtained  from  the  particular  locality  in  which  the  proposed  road 
is  to  be  operated  will  be  found  of  more  value.  The  nearer  the 
conditions  of  installation  and  operation  of  these  roads  approach 
those  of  the  proposed  road,  the  more  dependable  will  be  the 
results  based  thereon. 

A  table  giving  data  of  value  in  predetermining  the  traffic  and 
gross  income  for  a  proposed  road  is  given  herewith  for  cities  of 
the  middle  west  under  25,000  population. 


TABLE  II. 
Electric  Railway  Statistics.^ 


No.  passen- 
gers per  unit 
population. 


Miles  track 
Total,      per   looo 
population. 


Alton,  North  Alton,  Up-  17,487 

per  Alton,  111. 

Cairo,  111 12,566 

Kankakee,  Bradley,  Bour-  15,708 

bonnais.  III. 

\'incennes,  Ind 10,249 

Burlington,  la 23,201 

Ashtabula,  O 12,949 

Lima,  O 21,723 

Tiffin,  O 10,989 

Zanesville,  O 23,538 


1,497.130 


870,838 
714,769 


85.6 

69  3 

45-5 


12.25 


9.67 


450,000 

43-9 

8.00 

1,600,000 

69.0 

14-50 

999,857 

77.2 

5-75 

1,375,979 

63 -3 

18.55 

482,000 

43-9 

7-33 

1,800,000 

76.5 

10.00 

0.70 

077 
0.81 

0.78 

0.62 

0.44 

0.85 

0.67 
0.42 


Whereas  such  a  table  ofifers  more  opportunity  for  the  correct 
comparison  of  traffic,  etc.,  for  an  urban  road  or  for  extensions 
to  such  a  system  than  for  the  predetermination  of  interurban 
traffic,  yet  the  methods  outlined  may  be  used  to  advantage  in 
interurban  developments  providing  they  are  applied  with  con- 
servative judgment  based  upon  successful  interurban  experience. 
As  an  example  of  such  adaptation  of  data  to  interurban  practice 
it  should  be  noted  that  a  different  proportion  of  terminal  popula- 
tion will  be  tributary  to  the  traffic  of  the  proposed  road  in  each 

'  Taken  from  Railway  Census,  1902. 


TR_\FFIC    STUDIES.  I  5 

case  under  consideration.  In  the  case  of  the  road  being  the 
first  to  enter  a  relatively  small  terminal  city,  a  large  portion  of 
the  population  of  the  city  will  avail  itself  of  the  road,  but  if  the 
road  is  the  fifth  or  sixth  to  enter  such  a  city,  as  Indianapolis  or 
Chicago,  a  relatively  small  portion  of  the  population  of  the  termi- 
nal city  can  be  counted  upon  for  passenger  traffic.  It  follows 
directly  from  this,  therefore,  that  with  a  large  terminal  city, 
the  earnings  of  the  road  per  capita  "of  terminal  population  will 
be  small  and  the  earnings  of  a  successful  road  per  mile  of  track 
will  be  relatively  large  and  vice  versa. 

Growth  in  Population. — It  is  necessary,  however,  to  know 
more  than  the  present  terminal  and  tributary  population.  The 
growth  of  both  for  several  years  to  come  must  be  predicted.  In 
order  to  do  this  intelligently  it  is  necessary  to  know  the  growth 
in  the  past  not  only,  but  to  study  the  causes  of  any  eccentricities 
in  the  growth  curve.  It  is  only  after  such  a  detailed  study  that 
the  population  curve  may  be  accurately  extended  to  determine 
the  population  to  be  expected  forty  or  fifty  years  hence. 

Bion  J.  Arnold,  consulting  engineer  of  Chicago,  in  his  "Re- 
port on  the  Chicago  Transportation  Problem,"  points  out  very 
clearly  the  fallacy  of  predicting  the  population  for  any  consider- 
able term  of  years  by  any  rate  of  growth  which  has  existed  in  the 
past,  if  the  law  of  "Yearly  decrease  in  the  rate  of  increase"  be 
neglected.  If,  by  way  of  illustration,  we  refer  to  the  curve  of 
Fig.  I  which  represents  the  population  of  the  city  of  Phila- 
delphia during  a  long  term  of  years,  we  shall  see  -at  once  that 
had  the  future  population  of  that  city  been  predicted  in  i860 
from  the  rate  of  increase  during  the  pre\ious  decade,  the  result 
would  have  been  far  from  the  fact.  As  a  matter  of  fact,  the  rate 
of  increase  in  population  of  Philadelphia  dropped  in  five  years 
from  T^T^  per  cent,  per  annum  to  9.7  per  cent,  and,  in  another 
five  years,  to  2.9  per  cent.  Although  this  marked  change  in  the 
rate  of  increase  of  population  is  exceptional  in  the  case  of  Phila- 
delphia, Arnold  found  that  in  the  cases  of  the  eight  largest  cites 
of  the  world  which  he  studied  the  average  rate  of  increase  in 
population  is  gradually  decreasing.  It  is  obvious,  therefore, 
that  even  if  the  average  rate  of  increase  in  population  over  a 
long  term  of  years  were  applied  to  the  future  growth  of  a  city, 


i6 


ELECTRIC    RAILWAY    ENGINEERING. 


the  results  would  still  be  too  high.  As  an  illustration,  the 
average  rate  of  increase  in  Chicago  from  1837  to  1902  was  8.6 
per  cent,  per  annum,  from  1892  to  1902  it  was  4.9  per  cent.,  and 
during  the  year  1902  it  was  7.7  per  cent.  Beginning  with  the 
year  1900  and  compounding  the  population  at  5  per  cent.,  the 
resulting  value  for  the  year  1952  would  be  18,500,000,  while  an  8 


2,100.000 

1,950,000 

1,800,000 

1,&50,000 

1,500,000 

1,350,000 

1,200,000 

1,050,000 

900,000 

750,000 

000,000 

450,000 

300,000 

150,000 


POPULATION 

OF  CITY  OF 

PHILADELPHIA 

1800-1900 

y 

A 

^Jt 

■ 

^ 

A 

1 
1 

^, 

"S".:?' 

1 

?4 

-H      W 


Fig.  I. 


per  cent,  increase,  compounded,  would  give  this  city  a  population 
of  26,500,000  in  only  35  years.  With  the  use  of  the  more  correct 
method,  however,  which  takes  into  consideration  the  fact  that 
the  rate  of  increase  is  continually  on  the  decline,  the  population  is 
compounded  with  a  constantly  decreasing  percentage.  Such  a 
method  applied  to  the  city  of  Chicago  and  beginning  with  the  1902 


TRAFFIC    STUDIES. 


17 


rate  of  7  per  cent,  results  in  a  predicted  population  of  13,250,000 
for  the  year  1952.  It  is  probable  that  this  will  mark  the  upper 
limit  of  the  actual  population  curve,  while  the  minimum  limit 
of  the  area  within  which  the  population  will  fall  in  the  next  fifty 
years  will  be  determined  by  a  similar  method  of  reasoning  begin- 
ning with  an  increase  rate  of  3  per  cent. .which  represents  the 


4,(joO,000 
4,500,000 

4,350,000 
4,300,000 
4,060,000 
3,900,000 
3,750,000 
3,000,000 
3,450,000 
3,300,000 
3,150,000 
3,000,000 
2,850,000 
2,700,000 


i 

1 

POPULATION  OF 
CITY  OF 
LONDON 
1861-1901 

L 

4 

/ 

•*/ 

\ 

flu 

i 

i 

'I 

i 
i 

*^7 

■i 

1/ 

f 

Fig. 


average  growth  of  the  large  European  cities.  The  result  of  the 
latter  calculation  gives  Chicago  a  population  of  5,250,000  in  1952. 
Reference  to  Figs.  2,  3,  and  4  will  give  an  idea  of  the  changing 
rates  of  increase  in  population  of  the  cities  of  London,  Paris,  and 
New  York  respectively.  Several  decades  will  be  noted  in  these 
curves  durino-  which  these  rates  have  been  abnormal;  which  rates, 


i8 


ELECTRIC    RAILWAY    ENGINEERING. 


if  used  as  a  basis  for  the  predetermination  of  future  population, 
would  lead  to  very  erroneous  results. 

Riding  Habit.— The  proper  determination  of  the  "riding 
habit"  for  a  given  community  or  the  number  of  passengers  per 
capita  of  population  per  annum  is  important  if  the  traffic  of  a 
proposed  road  is  to  be   correctly  predicted.     This  is  always  a 


Fig.  3. 


local  problem,  dependent  upon  the  geographical  and  industrial 
features  of  the  country  or  city  under  consideration,  as  well  as 
upon  the  customs  of  the  people,  the  existing  or  possible  forms  of 
recreation,  etc.  In  the  case  of  the  interurban  road  little  aid 
can  be  obtained  from  tabulated  results  upon  other  roads  for 
the  possibility  of  comparison  with  a  road  where  the  conditions 


TRAFFIC    STUDIES. 


19 


outlined  above  are  the  same  is  very  small.  For  urban  roads, 
however,  reference  may  well  be  made  to  a  curve  (Fig.  5),  plotted 
between  "passengers  per  capita  per  annum"  and  population 
throughout  the  country.  This  curve  has  been  shown  by  one 
author'  to  rise  from  approximately  seventy  passengers  per  capita 


2,100,000 

1,950,000 
1,800,000 
1,650,000 

POPULATION 

OF  CITY  OF 

NEW  YORK 

1800-1890 

-^3:i- 

h 

1,350,000 
1,200,000 

5^ 

•s 

■f    / 

1,0.jO,000 

4^ 

^ 

/ 
.-^1 

'y4.5 

'' 

7oO,000 

..'^^ 

jj; 

f/ 

450,000 
300,000 

V 
A 

y-o.\ 

■/■ 

^^ 

Ui 

""^ 

5l' 

<A'^ 

Fig.  4. 


per  annum  in  cities  of  15,000  population  to  a  constant  x'alue  of 
240  in  cities  of  1,000,000  inhabitants  and  over,  although  Arnold's 
results  in  Chicago  show  an  increase  from  150  to  182  passengers 
per  capita  per  annum  from  1891  to  1901. 

Competition. — The  question  of  com])etiti()n  with  steam  roads 

'  See  "Electric  Railways,"  Vol.  II,  by  S.  \V.  Ashe. 


20 


ELECTRIC    RAILWAY   ENGINEERING. 


is  a  vital  one  with  most  interurban  and  suburban  railroads, 
whereas  most  urban  systems  are  practically  monopolies. 

If  the  proposed  road  is  to  parallel  a  steam  line,  it  is  usually 
advisable  to  make  a  study  of  the  trafi&c  conditions  on  such  an 
existing  line,  either  from  authentic  records  or  by  actual  counting 
of  passengers  on  all  trains  in  the  various  seasons  of  the  year. 
Such  records  must  be  applied  with  great  caution,  however,  for 
it  has  been  found  that  a  well  equipped  interurban  line  with  fre- 
quent and  high  speed  ser\'ice  often  takes  away  much  local  traffic 


—i— i — 

1 

— 

^ 

220 

^ 

^ 

■^ 

200 

^ 

^ 

«180 

/ 

/ 

I*  160 

/ 

/ 

RELATION  OF  ANNUAL  PASSENGERS 
PER  CAPITA  TO   POPULATION. 

V 

/ 

^  140 

/ 

a 

, 

' 

by  120 

/ 

o 

/ 

iSlOO 

/ 

^ 

1 

2  so 

j 

a 

<<  60 

• 

40 

ao 

500,000 


1.000,000 


1,500,000 


Population 
Fig.   5. 


from  the  parallel  steam  lines  not  only,  but,  in  addition,  creates  a 
traffic  of  its  own.  In  other  words,  if  the  public  can  make  a 
trip  at  any  time  of  the  day  desired;  if  the  cars  are  clean,  free  from 
smoke  and  cinders,  and  comfortable,  and  if  the  time  lost  en  route 
is  a  minimum,  it  has  been  found  that  many  ride  who  would  other- 
wise remain  at  home.  It  is  difficult  to  obtain  more  than  a  very 
rough  approximation,  therefore,  of  future  traffic  from  steam  rail- 
road statistics.  That  preference  is  given  to  the  electric  road  and 
that  traffic  is  often  greatly  reduced  on  existing  steam  lines  with 


TRAFFIC    STUDIES.  21 

the  advent  of  the  electric  interurbcan  Hne  is  clearly  shown  by  the 
figures  on  the  following  table. 

TABLE  III. 


TR.4FFIC  ON  Lake  Shore  axd  Michigan  Southern  Between  Cleveland  and 

Oberlin  ' 

Average  per 

Westbound.          Eastbound.               Total.                   month 

1895 

1902 

104,426                   98,588                 203,014                   16,918 
46,328                   45,433                   91,761                     7,647 

Gross  Income. — After  having  studied  all  statistics  and  local 
conditions  which  may  possibly  have  a  bearing  upon  the  future 
traflic  of  a  proposed  road  and  ha\dng  approximated  from  such 
study,  combined  with  the  riding  habit  of  the  people,  the  total 
traffic  that  may  be  expected  with  its  hourly,  daily,  and  season 
wide  fluctuations,  it  will  be  necessary  to  determine  the  gross  in- 
come possible  from  such  a  road.  This  may  be  done  either  by 
applying  the  average  fare  paid  per  passenger  to  the  above  trafiiic 
figures,  which  total  may  be  augmented  in  some  cases  by  express, 
freight,  and  mail  receipts;  or  a  comparison  may  be  made  with 
other  similar  roads  operating  successfully  in  the  same  locality  and 
under  similar  conditions.  Such  a  comparison  based  upon  units 
of  gross  income  per  capita  of  terminal  or  tributary  population  or 
per  mile  of  track  gives  very  satisfactory  results,  as  will  be  seen 
from  the  following  example. 

In  determining  the  gross  income  for  a  proposed  fifty  mile 
electric  interurban  line  in  Texas,  connecting  cities  of  34,000  and 
58,000  inhabitants,  comparison  was  made  with  two  other  roads 
operating  under  similar  conditions  with  the  following  results. 

One  of  these  roads,  in  the  same  state,  connected  cities  of  15,000 
population  each  with  16  miles  of  track,  returning  a  gross  income 
in  1905  of  $3.48  per  capita  of  terminal  population,  while  the 
second  road,  81  miles  in  length,  connecting  cities  of  26,000  and 
52,000  population,  earned  a  gross  income  of  $8.45  per  capita. 
Taking  the  more  conservative  value  of  $3.48  from  the  former 

'  See  "American  Electric  Railway  Practice,"  by  Herrick  and  Boynton,  p.  4. 


22  ELECTRIC    RAILWAY    ENGINEERING. 

road  as  a  basis,  the  minimum  return  from  the  new  road  should 
be  approximately  92000XS3.48  or  $321,000,  representing  an 
earning  of  $6,420  per  mile.  This  figure  compares  very  favorably 
with  the  corresponding  values  of  $8, 160  and  $6,540  per  mile 
for  the  two  roads  j)reviously  referred  to. 

In  order  to  determine  the  net  income  it  would  be  possible,  of 
course,  to  approximate  the  operating  expenses,  fixed  charges, 
etc.,  in  detail,  and  subtract  them  from  the  gross  income.  A  fair 
average  ratio  of  net  to  gross  income  is  often  taken,  however,  as 
45  per  cent.  This  figure  applied  to  this  particular  road  shows  a 
net  income  of  §144, 500  annually  and  therefore  a  possible  operating 
expense  of  $176,500. 

Number  and  Capacity  of  Cars. — The  determination  of  the 
number  and  therefore  the  necessary  carrying  capacity  of  cars  is 
sometimes  arrived  at  as  follows:^ 

A  well  conducted  road  may  safely  be  assumed  to  earn  twenty 
cents  per  car  mile.  The  car  mileage  per  year  may  therefore  be 
roughly  obtained  by  di^^ding  the  gross  income  by  the  factor  (o .  2) 
The  number  of  car  miles  per  hour  are,  of  course,  readily  deduced 
from  the  above  quotient  by  di\iding  by  the  hours  of  actual  car 
operation  per  year.  If,  then,  the  average  schedule  speed  is  speci- 
fied by  city  ordinance  or  is  decided  upon  by  the  railway  officials, 
the  number  of  cars  may  readily  be  determined  from  the  equation 

Car  miles  per  hour. 

Number  of  cars  =  — ,     —,  —        r, : 

Schedule  speed  m  miles  per  hour. 

However,  the  above  result  can  be  more  satisfactorily  and  correctly 
obtained  in  most  cases  from  train  schedules.  The  total  traffic 
to  be  expected  having  been  calculated  as  explained  above,  the 
headway  or  schedule  speed  of  cars  is  usually  readily  decided  upon 
with  a  Wew  toward  carrying  this  amount  of  traffic  or  in  ordei  to 
successfully  meet  the  competition  of  parallel  steam  roads.  The 
graphical  train  schedule  sheet  explained  in  detail  in  Chapter  IV 
may  then  be  plotted,  whereupon  the  number  of  cars  necessary  to 
maintain  the  proposed  schedule  immediately  becomes  apparent. 
It  would  be  possible,  of  course,  to  deteimine  the  seating  capacity 
and  size  of  cars  to  be  purchased  for  a  given  road  from  the  theo- 

'  See  "Electric  Railways"  by  S.  W.  Ashe,  p.  i6,  Vol.  II. 


TR.AFFIC    STUDIES.  2^ 

retical  calculation  of  the  probable  number  of  passengers  per  trip 
at  various  times  of  day  and  at  various  seasons  of  year  but  such 
calculations  seldom,  if  ever,  become  controlling  features  in  the 
purchase  of  cars  for  a  given  road.  For  interurban  roads  the  size 
and  capacity  of  cars  have  been  very  well  standardized  by  custom, 
the  increased  traffic  at  times  being  handled  by  changes  in  schedule 
or  by  the  operation  of  two  or  more  cars  together  in  a  train  on 
the  same  schedule.  As  will  be  seen  in  the  following  chapter, 
however,  cars  are  seldom  operated  at  their  exact  seating  capacity 
and  in  spite  of  the  fact  that  standing  in  cars  on  interurban  trips 
becomes  most  tedious  and  oppressive  and,  granting  the  conclusions 
discussed  more  at  length  in  the  following  pages  that  a  consider- 
able percentage  of  passengers  stand  in  cars  by  preference,  yet 
it  is  a  regrettable  fact  that  the  size  and  headway  of  cars  on  many 
roads,  especially  in  cases  of  urban  traffic,  are  determined  with 
but  little  consideration  of  the  ratio  of  seating  capacity  to  pass- 
enger traffic. 


CHAPTER  III. 
Traffic  Studies  (Existing). 

The  necessity  of  making  a  careful  study  of  existing  trafiEic  upon 
urban,  interurban,  and  even  steam  railroads  for  the  purpose  of 
comparison  with  the  conditions  of  a  proposed  line  and  in  order 
to  intelligently  predetermine  the  probable  income  from,  and 
therefore  the  advisability  of  financing  and  building  a  new  line, 
has  already  been  set  forth.  Further  than  this,  those  responsible 
for  the  successful  operation  of  present  and  future  lines  must 
continually  study  the  condition  and  tendencies  of  traffic.  Quot- 
ing from  a  recent  editorial  in  the  Street  Railway  Journal  upon 
this  point,  "The  managers  of  city  railway  systems  which  do  not 
embrace  more  than  a  half-dozen  routes  usually  feel  that  they 
know  every  detail  of  the  trafhc  distribution  so  well  that  it  is 
unnecessary  to  go  to  the  trouble  of  preparing  graphic  records. 
The  correctness  of  this  point  of  -siew,  however,  is  not  proved  by 
the  experience  of  those  who  have  had  occasion  to  prepare  traffic 
curves,  even  for  cities  of  less  than  40,000  population,  as  they 
have  found  that  such  curves  will  betray  the  riding  peculiarities  of 
the  public  much  more  clearly  than  a  mere  tabulation.  From  such 
a  record,  for  example,  it  is  easy  to  observe  whether  the  passengers 
take  kindly  to  short  trip  cars  or  neglect  them  in  favor  of  through 
cars  even  when  they  do  not  ride  to  the  end  of  the  line. 

"Traffic  curves,  furthermore,  are  not  only  of  value  to  the  com- 
pany in  making  up  its  schedule,  but  are  also  an  aid  in  its  relations 
to  the  public.  When  a  complaint  is  made  about  the  service  on  a 
certain  line,  it  is  surely  convenient  to  be  able  to  prove  graphically 
that  in  the  course  of  the  day's  operation  the  number  of  seats 
furnished  far  exceed  the  passengers  and  that  the  schedules 
adopted  are  based  strictly  upon  the  amount  of  traffic  which  the  line 
brings." 

While  reports  of  traffic  investigations  have  been  made  public 
from  time  to  time,  especially  as  the  results  of  studies  by  consulting 

.    24 


TRAFFIC    STUDIES. 


engineers  in  connection  with  proposed  improvements  to  the  rail- 
way system  for  the  purpose  of  reducing  congestion  of  traffic  by 
means  of  subways,  elevated  lines,  rerouting  of  cars,  introduction 
of  prepayment  cars,  etc.,  yet  little  has  been  said  regarding  the 
best  methods  of  making  such  detailed  studies  with  any  degree  of 
accuracy.  In  fact  the  difficulty  in  obtaining  accurate  and  de- 
pendable results  has  often  been  given  as  an  excuse  for  not  under- 
taking such  a  study.  It  is  also  true  that  where  conditions  of 
traffic  are  most  variable,  and  these  difficulties,  therefore,  most 
pronounced,  the  need  of  such  an  investigation  is  usually  greatest 
and,  when  undertaken,  results  in  the  greatest  possible  improve- 
ment in  ser^dce. 

It  has  been  found  where  these  traffic  studies  have  been  success- 
fully made  that  it  is  necessary  to  obtain  data  entirely  independent 
of  the  daily  returns  of  employees  and  that  these  data  should  be 
obtained  by  a  crew  of  technically  trained  observers  who  under- 
stand the  significance  of  every  reading  taken.  The  average 
car  employee,  no  matter  how  loyal  and  conscientious,  usually 
not  understanding  the  use  to  be  made  of  the  data  collected  and 
the  relative  accuracy  with  which  the  various  readings  should  be 
taken,  has  been  found  unsatisfactory  for  this  work. 

It  is  usually  advisable  to  subdivide  the  city  roughly  into  dis- 
tricts such  as  business,  manufacturing,  residence,  etc.,  and  then 
to  make  a  detailed  study  of  the  riding  habits  of  the  people  and 
the  loading  of  the  cars  on  a  single  route  or  division  at  a  time. 
It  will  at  once  be  observed  that  the  day  may  readily  be  divided 
into  several  periods  of  peak  load,  usually  four  in  number.  One 
city  whose  traffic  conditions  were  investigated  recently  by  the 
Wisconsin  State  Commission  was  found  to  have  its  four  periods 
of  peak  load  extending  from  6.00  to  9.00  a.  m.,  ii.oo  a.  m.  to  2.00 
p.  M.,  5.00  to  8.00  p.  M.,  and  from  10.00  to  11.00  p.  m.,  respectively.^ 
The  last  was,  of  course,  the  theatre  period  and  was  therefore 
limited  to  a  small  district  of  the  city. 

In  studying  the  problem  further,  it  is  usually  found  that  the 
public  at  large  has  a  very  well  defined  habit  of  travel  which 
does  not  vary  greatly  from  one  end  of  the  year  to  another.  Pleas- 
ure seekers  and  shoppers,  of  course,  are  irregular  in  their  move- 

^  Graduate  Thesis,  Purdue  University,  1910,  by  R.  W.  Harris. 


26  ELECTRIC    ILMLWAY    ENGINEERING. 

ments,  but  the  majority  of  passengers  will  soon  be  found  to  follow 
a  definite  route  in  their  traveling,  not  only,  but  certain  classes 
may  be  depended  upon  to  ride  during  certain  periods  of  the  day. 
The  above  mentioned  residence  districts  of  the  city  and  the  pass- 
engers as  well  may,  therefore,  be  still  further  subdivided  as 
follows : 

1.  Business  or  professional. 

2.  Clerk  and  shoppers. 

3.  Laborers. 

With  such  classifications  in  mind,  it  is  necessary  that  the 
inspectors  ride  over  the  route  or  division  under  investigation  a 
number  of  times  during  all  periods  of  the  day  and  in  all  kinds  of 
weather  to  note  roughly  the  effects  of  time  of  day,  weather,  and 
all  local  conditions  upon  maximum  traffic.  Especial  notice 
should  be  taken  of  the  stops  which  are  of  most  importance,  i.e., 
those  at  which  most  passengers  leave  and  board  cars. 

After  such  preliminary  study  the  number  of  inspectors  neces- 
sary, the  particular  stops  to  be  studied,  data  to  be  recorded,  and 
the  number  of  readings  to  be  taken  in  the  detailed  investigation 
may  be  decided  upon.  These  readings  may  be  taken  by  in- 
spectors, provided  with  stop  watches  located  at  the  principal 
stopping  points;  or,  if  the  number  of  cars  is  not  too  great,  an 
inspector  may  be  assigned  to  each  car  on  the  route.  In  general 
the  observations  to  be  made  at  the  most  important  stops  are  as 
follows : 

1.  Line  (route). 

2.  Period  of  day. 

3.  Exact  time. 

4.  Direction  of  car. 

5.  Number  of  car. 

6.  Total  number  of  people  on  car. 

7.  Number  of  people  standing  in  front  vestibule. 

8.  Number  of  people  standing  in  rear  vestibule. 

9.  Number  of  people  getting  ofi  car. 

10.  Number  of  people  getting  on  car. 

11.  Class  of  passengers. 

12.  Conditions  of  vehicular  traffic. 

13.  Conditions  of  pedestrian  traffic. 


TR.\FFIC    STUDIES. 


27 


With  symbols  to  represent  many  of  the  above  conditions  upon 
data  sheets  carefully  prepared  in  advance  and  with  a  little  ex- 
perience on  the  part  of  the  inspector,  the  above  data  have  been 
found  to  be  readily  and  accurately  taken.  In  fact  in  the  investi- 
gations above  alluded  to  check  observations,  taken  independently 
but  at  the  same  time  and  place,  varied  less  than  5  per  cent.  This 
is  sufficientlv  accurate  for  the  determinations  desired. 


1          1          1          1          I          I           1 

CAR  DEMAND  CURVES 

80- 

/ 

^ 

TO- 

/ 

I 

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y 

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0  60 

/' 

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uforta 

)le^ 

Load 

u  50 

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[  Mixed  1,;  2,  3  Class  Res. 

1      30                   40 

1             Blocks 

1         (10  Blocks  =  1  Mile 

Dii 

c-         r.                                               I 

i      50            ;       60 

1             l-Out 

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Srd  Class  Kes.  Dis/                                            j 

r^ ^^ 

Fig.  6. 


The  results  of  an  extensive  investigation  carried  on  in  this  wav 
in  one  of  the  large  cities  of  the  west  are  typified  by  the  single 
example  represented  by  Fig.  6,  in  which  the  shaded  areas  repre- 
sent the  various  districts  served  by  the  particular  car  line  under 
consideration,  while  the  ordinates  of  the  upper  curve  represent  the 
passengers  on  the  car  during  the  period  of  maximum  traffic  ex- 
tending from  5.00  to  8.00  p.  M.  The  abscissae  of  both  curves 
represent  the  distance  in  miles  on  either  side  of  the  center  of  the 
city,  while  the  full  lines  and  dotted  lines  of  the  upper  curve 


28 


ELECTRIC    RAILWAY   ENGINEERING. 


represent  out-going  and  in-coming  cars,  respectively.  It  will  be 
readily  seen  that  the  traffic  at  this  time  of  day  is  largely  from  the 
city  outward,  as  would  be  expected.  Another  point  of  significance 
is  the  fact  that  out-going  cars  from  G  to  A  take  on  the  greater 
portion  of  their  passengers  between  G  and  E  which  is  the  retail 
business  district  of  the  division,  and  deposit  them  principally 
between  C  and  A  which  is  in  the  mixed  residence  district.  These 
passengers  may  properly  be  classed  therefore  as  "clerks  and 
shoppers."     On  the  other  hand  the  cars  running  from  G  to  K 

be  5J 


1 

a 

1 

1 

PASSENGERS  STANDING  BY  PREFERENCE 

^ 

(T) 

1 

O 

iS 

P4 

R 

40 

^ 

^ 

y 

y 

3o 

y 

y 

30 

y 

y 

- 

y 

\y 

25 

V 

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\ 

y 

X 

, 

?n 



_ 

A- 

N 

ti. 

■^ 



, 









L 

~i^ 

^ 

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— 

^ 

_ 

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ss. 

15 

— 

- 

=^ 

=- 

1^ 

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0 

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=- 

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— 

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as*' 

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1-4 


r9  10-U         15-19       20-24        25-;39 

Total  Number  of  Passengers  on  Car 


30-34        35-39        40-42 


Fig.  7. 


take  on  their  passengers  between  G  and  H  within  the  wholesale 
business  and  manufacturing  districts  and  deposit  them  between 
I  and  K  in  the  third  class  residence  district.  This  leads  us  to 
classify  this  traffic  as  "laborers."  In  a  similar  manner  it  is 
possible  to  determine  from  curves  resulting  from  careful  investi- 
gation the  tendency  and  amount  of  traffic  on  each  division  at  all 
times  of  day. 

In  order  to  determine,  however,  whether  or  not  sufficient  cars 
of  ample  capacity  are  being  supplied,  the  "comfortable  load" 
per  car  must  be  decided  upon.  During  such  investigations  in 
several  of  the  larger  cities  it  has  been  found  that  a  considerable 


TRAFFIC    STUDIES.  29 

number  of  the  passengers  on  a  car  stand  by  preference.  In  Fig.  7, 
curves  A  and  A'  show  the  total  and  percentage  increase  respec- 
tively of  passengers  standing  by  preference  as  the  number  of 
passengers  on  the  car  increases  in  a  city  of  25,000  population, 
while  curves  B  and  B'  show  curves  of  similar  tendency  for  a 
city  of  330,000  in  the  Middle  West.  Referring  to  curve  B  and 
with  the  knowledge  that  the  cars  operated  in  this  city  will  seat 
42  passengers,  it  will  be  noted  that  when  the  car  is  fully  loaded, 
eight  will,  on  the  average,  stand  by  preference.  The  comfortable 
load  has  therefore  been  taken  as  50  passengers  and  the  variation 
of  the  "car  demand"  curves  of  Fig.  6  above  and  below  the 
''comfortable  load"  line  indicates  at  once  the  quality  of  service 
being  rendered. 

It  cannot  be  reasonably  expected  by  the  public  that  sufficient 
cars  shall  be  furnished  to  enable  every  one  to  have  a  seat  at  all 
times  of  day,  for  many  of  the  peak  loads  come  on  so  suddenly 
and  often  so  unexpectedly  that  it  would  be  impossible  to  have  the 
necessary  cars  at  the  proper  time  and  place  if  it  were  the  policy 
of  the  company  to  accomodate  the  peak  traffic  with  seats.  Most 
progressive  companies,  however,  endeavor  to  meet  the  just  de- 
mands of  the  riding  public  and  therefore  should  determine  those 
demands  from  time  to  time  by  methods  similar  to  those  outlined 
above. 


CH.\PTER  lY. 
TR.4IN  Schedules. 

Having  studied  in  the  two  previous  chapters  the  important 
elements  underlying  the  determination  of  probable  traffic  on  a 
new  railway  line  or  upon  the  extension  to  an  old  system,  it  becomes 
necessary  to  establish  the  train  schedule.  As  has  been  previously 
inferred,  this  is  often  a  question  of  judgment  to  be  exercised  by 
the  executive  head  of  the  road  in  view  of  the  necessity  of  meeting 
competition.  That  is  to  say,  the  engineer  who  platis  the  details  of 
the  train  schedule  is  instructed  to  arrange  for  hourly  or  half 
hourly  interurban  service,  as  the  case  may  be,  or  the  headway  ex- 
pressed in  minutes  or  distance  between  cars  in  feet  may  be  spec- 
ified in  the  urban  system.  In  both  types  of  system  the  limiting 
schedule  speed  is  usually  stipulated,  often  by  the  municipalities  in- 
volved. The  interurban  system  is  usually  limited  to  two  or  more 
different  schedule  speeds,  the  higher  velocities  being  confined  to 
operation  over  private  right  of  way  and  the  lower  within  city 
limits  or  upon  particularly  dangerous  sections  of  track  such  as 
trestles,  draw-bridges,  and  temporary  construction. 

Whereas  the  hours  of  train  arrival  and  departure  arc  usually 
placed  in  the  hands  of  the  public  in  the  form  of  time  tables, 
the  most  convenient  and  common  form  for  the  study  of  these 
data  by  railway  engineers  is  the  graphical  chart.  Many  factors 
entering  into  the  proper  construction  and  successful  operation  of 
a  road  are  at  once  apparent  from  such  a  chart  or  graphical  train 
schedule.  This  train  schedule  is  often  plotted  with  time  of  day 
in  hours  and  minutes  as  ordinates  and  distances  expressed  in  miles 
as  abscissae.  It  is  convenient  if  the  ordinates  representing  the 
hours  be  designated  by  heavy  lines  on  the  coordinate  paper  and 
if  the  hourly  sections  be  subdivided  into  sixths  or  twelfths,  repre- 
senting ten  and  five  minute  intervals  respectively.     Upon  the 

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INTERURBAN  TRAIN  SCHEDULE   (preliminary) 


TILMX    SCHEDULES.  3 1 

distance  scale  it  is  customary  to  designate  the  distance  between 
stations  and  the  location  of  any  points  of  especial  engineering 
interest  along  the  line  such  as  branch  lines,  railway  crossings, 
city  and  township  limits,  etc.     With  the  scales  of  coordinates 
thus  determined,  a  series  of  slanting  lines,  Fig.  8,  may  be  drawn 
to  represent  the  progress  of  the  train  from  station  to  station. 
The  slope  of  these  lines  is,  of  course,  dependent  upon  speed,  the 
co-tangent  of  the  angle  which  they  make  with  the  horizontal 
representing  the  schedule  speed  of  the  train.     A  chart  made  up  of 
such  straight  lines  representing  each  train  leaving  the  terminals 
of  the  line  in  either  direction  is  sufficiently  accurate  for  a  rough 
preliminary   study   of   traffic   possibilities,   power  requirements, 
and  substation  locations,  but  before  exact  time  tables  can  be 
adjusted  and  meeting  points  determined,  a  very  much  more  ac- 
curate and  detailed  graphical  train  schedule  must  be  drawn. 
Such  a  schedule  involving  three  different  schedule  speeds  over  the 
various  sections  of  road  as  well  at  the  representation  of  the  time 
elapsed  in  making  station  stops,  is  shown  in  Fig.  9,  which  is  the 
proposed  train  schedule  for  a  50.6  mile  interurban  line,  planned 
to  connect  the  cities  of  Galveston  and  Houston,  Texas,  within 
whose  limits  the  schedule  speed  was  confined  to  10  m.  p.  h.     It 
should  be  noted  that  speeds  of  30  m.  p.  h.  and  55  m.  p.  h.  are 
adopted  for  portions  of  the  private  right  of  way,  while  one  minute 
has  been  allowed  for  the  average  station  stop.     Such  a  graphical 
schedule  enables  one  to  predetermine  not  only  the  number  of 
cars  necessary  to  maintain  a  given  schedule  and  the  position  of 
those  cars  at  any  moment,  but  it  locates  the  meeting  points, 
which  are  designated  by  the  crossing  of  the  schedule  lines,  and, 
when  used  in  conjunction  with  the  power  curves  of  the  various 
cars,  it  aids  in  locating  substations  and  in  determining  the  average 
and  maximum  loads  on  substations  and  power  station.     Com- 
paring Figs.  8  and  9  it  will  be  noticed  that  while  the  former  has 
the  same  through  schedule  speed  as  the  latter  and  while  all  con- 
siderations based  upon  the  headway  and  the  time  of  leaving  and 
arrival  at  terminal  cities  taken  from  Fig.  8  are  quite  as  accurate 
as  those  taken  from  the  more  detailed  chart,  Fig.  9,  yet  it  is  clear 
that  nothing  of  value  can  be  learned  from  the  former  regarding 
the  meeting  points  nor  the  positions  of  trains  at  anv  moment. 


32  ELECTRIC    RAILWAY    ENGINEERING. 

Although  local  conditions  will  prevent  any  extensive  com- 
parison of  train  schedules  of  different  roads  or  even  the  schedules 
of  the  same  road  at  different  seasons  of  year,  yet  it  is  believed 
that  the  principal  factors  to  be  borne  in  mind  in  plotting  schedules 
can  best  be  outlined  by  a  more  detailed  study  of  the  particular 
schedule  of  Fig.  9. 

This  schedule  is  one  proposed  for  maximum  summer  traffic. 

It  has  not  been  tried  out  in  actual  operation,  and  it  is  quite 

probable  that  hourly  headway  in  place  of  the  half  hourly  train 

spacing  will  best  meet  the  demand.     It  will  be  noted  that  the 

first  trains  in  the  morning  leave  both  terminals  simultaneously 

at  6.00  A.  M.,  and  make  the  run  in  one  hour  and  forty-five  minutes 

111,              1      r  50.6x60 
requirmg   a   through   schedule   speed  of     =29  m.  p.  h. 

Further  reference  to  the  schedule  will  show  that  of  this  total  time 
only  43  minutes  is  spent  on  the  private  right  of  way  where  the 
maximum  speed  of  55  m.  p.  h.  is  possible.  While  all  trains  stop 
at  all  stations  within  the  city  limits,  there  are  a  number  of  flag 
stops  between  these  limits  which  tend  to  make  the  operating 
schedule  irregular  but  which  for  convenience  in  plotting  can  be 
represented  fairly  accurately  by  allowing  three  flag  stops  for 
each  train  between  the  Southern  Pacific  Railway  crossing  and 
that  of  the  T.  C.  T.  Co.,  at  which  crossings  all  trains  are  required 
to  stop. 

The  corresponding  points  of  meeting  as  graphically  deter- 
mined fall  sufficiently  close  together  to  be  provided  for  by  the  six 
sidings  shown  at  B,  C,  D,  E,  F,  G,  which  are  approximately 
I  mile  in  length.  These  could  be  materially  shortened  by  vary- 
ing the  running  time  slightly.  The  meeting  places  within  the 
city  limits  are  so  numerous  that  a  double  track  extending  from 
6  to  7  miles  out  of  the  city  terminals  would  seem  advisable  from 
this  preliminary  study. 

The  time  table  below,  which  was  taken  from  the  graphical 
schedule  represented  by  Fig.  9,  will  be  self  explanatory  and  a 
comparison  of  the  table  and  chart  will  illustrate  the  advantages 
of  the  graphical  method  even  if  the  time  table  were  to  be  the  only 
result  obtained  therefrom. 


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TRAIN    SCHEDULES.  ^^ 

TABLE  IV. 
Time  Table. 


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Genoa ^.  .  6.39  7  .08  7  .39  8.09  8.38  7  .04  7 

Webster *  .6.4817.187.488.188.49  6.557 

League  City 6.527  .21  7  .52  8.22  8.52  6.52  7 

Dickinson 6.56  7  .25  7  .57  8.26  8.56  6.47  7 

LaMarque 7  .05  7  .36  8.06  8.35  9.06  6.38  7 

Houston 7. 45  8. 15  8. 45  9. 15  9. 45  6.006 


It  has  been  previously  stated  that  one  of  the  advantages  of  the 
modern  interurban  system  in  competition  with  steam  roads  is 
its  ability  to  transport  the  passenger  to  more  nearly  the  exact 
point  in  a  terminal  city  to  which  he  wishes  to  go  and  often  gives 
him  transfer  privileges  upon  the  local  railway  system  if  necessary. 
When  comparing,  therefore,  the  graphical  train  schedule  of  the 
interurban  line  with  that  of  the  competing  steam  road,  especially 
with  regard  to  the  relatively  long  time  required  by  the  former 
within  the  city  limits,  it  is  often  advisable  to  add  to  the  steam 
schedule  the  walking  time  from  terminal  station  to  a  point  repre- 
senting the  average  destination  of  the  travelling  public  if  such 
can  be  found.  Such  "walking  schedule"  lines  added  to  the  train 
schedule  often  bring  out  very  striking  facts  in  favor  of  the  electric 
railway  as  a  popular  choice  of  means  of  transportation. 

The  particular  schedule  taken  for  illustration  is  a  relatively 
simple  one.  With  the  addition  of  limited  and  local  service  and 
possibly  freight  and  mail  trains,  and,  in  some  cases,  the  necessity 
of  meeting  the  schedules  of  trunk  or  branch  lines,  the  graphical 
chart  often  becomes  rather  complicated.  The  use  of  a  large 
scale  drawing,  however,  usually  pcrmhs  such  a  solution  to  be 
made  with  little  difficulty.  In  fact  such  schedules  have  been  very 
satisfactorily  used  with  the  varied  types  of  service  outlined  above, 
but  with  the  additional  requirement  that  the  train  be  made  up 
of  a  varying  number  of  cars  controlled  by  the  multiple  unit  system, 
the  various  cars  being  feeders  to  the  trunk  line  from  the  branches 
3 


34 


ELECTRIC    RAILWAY   ENGINEERING. 


en  route  and  being  joined  together  at  the  junction  stations,  thus 
forming  the  trains  to  enter  the  terminal  city.  The  trains  leaving 
the  terminal  city  would  operate  in  the  reverse  order,  dropping  car 
after  car  to  the  various  branches  and  having  relatively  few  through 
cars  from  terminal  to  terminal. 


CHAPTER  V. 
Motor  Characteristics. 

It  will  be  readily  recognized  that  the  ordinary  operation  of  a 
car,  whether  it  be  from  block  to  block  in  the  city  or  for  a  5  or  10 
mile  run  between  stations  on  an  interurban  private  right  of  way, 
may  be  subdivided  into  periods  of  acceleration,  constant  speed 
running,  coasting  deceleration,  braking  deceleration,  and  stop. 
The  conditions  of  particular  runs  as  to  length,  grades,  curves, 
etc.,  may  materially  vary  or  even  eliminate  some  of  these  periods, 
but  if  all  problems  of  car  operation  are  to  be  solved,  a  detailed 
study  of  each  of  these  portions  of  the  so-called  "speed  time  curve" 
must  be  undertaken. 

The  principal  factors  entering  into  the  determination  of  such 
a  curve  will  be  given  detailed  consideration  in  the  following  order, 
the  present  chapter  dealing  only  with  the  first  two  functions. 

Motor  characteristics. 

Gear  ratio. 

Weight  of  car. 

Bearing  and  rolling  friction. 

Air  resistance. 

Rotative  inertia  of  wheels  and  armatures. 

Grades. 

Curves. 

Brake  friction. 

Motor  Characteristics. — In  studying  the  characteristics  of 
motors,  in  order  to  determine  those  best  fitted  for  traction  service, 
it  may  be  found  convenient  to  classify  all  motors  into  the  follow- 
ing types: 

Direct  Current: 
Series, 
Shunt, 
Compound, 
Cumulative, 
Differential. 

35 


36  ELECTRIC    RAILWAY    ENGINEERING. 

Alternating  Current,  Polyphase: 

Induction, 

Synchronous. 
Alternating  Current,  Single  Phase: 

Series, 

Induction, 

Synchronous, 

Repulsion. 
If  the  speed  characteristics  of  all  these  motors  be  compared,  it 
will  be  found  that  with  varying  loads  within  the  rating  of  the 
motor  the  synchronous  motors,  both  single  and  polyphase, 
maintain  constant  speed,  while  all  the  other  direct  and  alternating 
current  motors  with  the  exception  of  the  series  type  operate  at 
nearly  constant  speed,  the  speed  falling  off  slightly,  usually  in 
accordance  with  a  straight  line  law,  as  the  load  increases.  The 
speed  characteristics  of  the  compound  motor  may  be  made  to 
approximate  those  of  either  the  series  or  shunt  motors  by  varying 
the  relative  strength  of  the  series  and  shunt  fields  respectively. 
Since  with  constant  potential  motors,  particularly  of  the  direct 
current  type,  the  current  input  to  the  motor  varies  approximately 
with  the  load,  the  speed-current  curves  of  Fig.  10  may  be  taken 
as  typical  of  the  three  classes  of  motors  designed  for  commercial 
service.  It  should  be  noted  that  all  of  these  motors  maintain  a 
speed  of  400  r.  p.  m.  at  their  rated  load  of  60  amperes,  thus  afford- 
ing a  basis  for  comparison. 

The  torque  of  a  motor,  which  is  defined  as  the  tangential  force 
that  the  armature  is  capable  of  exerting  at  a  radius  of  i  ft.  from 
the  center  of  the  shaft,  is  proportional  to  the  product  of  armature 
current  and  field  strength.  Since  the  field  strength  of  a  shunt 
type  constant  potential  motor  is  constant,  the  torc|ue  varies 
directly  with  the  armature  current  and  approximately  in  propor- 
tion to  the  load.  From  the  above  reasoning,  it  would  be  expected 
that  the  torque  of  a  series  motor  would  vary  with  the  square  of 
the  current  since  the  field  current  and  armature  current  are  the 
same.  In  the  actual  design  of  series  motors  for  railway  service, 
however,  the  magnetic  circuit  is  nearly  at  the  point  of  saturation 
except  at  very  light  loads.  The  torque-current  curve,  therefore, 
while  slightly  concave  upward  at  light  loads,  is  nearly  a  straight 


MOTOR    CHARACTERISTICS. 


37 


line  for  practically  all  operating  current  values  since  the  field 
strength  varies  but  slightly  with  change  of  current.  In  Fig.  1 1 ,  a 
comparison  of  the  torque-output  curves  of  the  three  types  of 
direct  current  motors  will  be  found. 

A  study  of  the  alternating  current  motors  will  reveal  the  fact 
that  all  types  except  the  series  have  approximately  the  same  inher- 


SPEED  CURVES  OF  REPRESENTATIVE 
TYPES  OF  MOTORS. 

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(50 


ent  characteristics  as  the  shunt  type  direct  current  motor,  if  the 
starting  conditions  of  some  of  the  former  be  disregarded.  The 
series  alternating  current  motor,  as  constructed  at  present  for 
railway  and  hoisting  service,  has  characteristics  very  closely 
approximating  those  of  the  series  direct  current  motor. 

In  order  to  determine  the  best  class  of  motor  for  traction  pur- 
poses, therefore,  it  is  only  necessary  to  apply  the  characteristics 


38 


ELECTRIC    RAILWAY    ENGINEERING. 


of  typical  shunt  and  series  direct  current  motors  to  the  conditions 
of  railway  service.  Such  characteristics  may  be  found  in  Fig. 
12  where  A  and  A'  are  the  speed  and  torc^ue  curves  of  a  series 
motor  while  curves  B  and  B'  represent   respectively  the  corre- 


100 


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TORQUE  CURVES  OF  REPRESENTATIVE 
TYPES  OF  MOTORS 


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sponding  characteristics  of  the  shunt  motor.  The  motors  from 
which  these  characteristics  were  taken  were  designed  for  the 
common  maximum  speed  of  22.8  m.  p.  h,  with  the  particular 
gear  ratio  used.     The  torque  is  expressed  in  terms  of  "pounds 


MOTOR    CiL\RACTERISTICS. 


39 


pull  at  periphery  of  car  wheel"  or  ''tractive  effort"  as  explained 
under  the  section  on  ''  Gear  Ratio." 

It  will  be  realized  at  once  that  a  car  under  most  conditions 
found  in  practice  must  be  able  to  operate  at  variable  speed. 
Conditions  of  grades,  curves,  pedestrian  and  vehicular  traffic, 
necessary  stops,  etc.,  demand  this.     With  the  geared  or  direct 


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SERIES  AND  SHUNT 
MOTOR  CHARACTERISTICS 

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connection  between  motors  and  car  axles  usually  adopted, 
therefore,  a  variable  speed  motor  seems  desirable.  Furthermore, 
a  much  larger  torque  is  required  to  start  and  accelerate  a  car  than 
is  necessary  to  maintain  the  car  at  full  speed.  As  the  power  taken 
by  a  motor  is  roughly  proportional  to  the  product  of  torque  and 
speed,  if  large  values  of  torque  cannot  be  obtained  at  low  speeds 


40 


ELECTRIC    RAILWAY   ENGINEERING. 


the  power  taken  by  the  motor  will  be  excessive.  Reference  to 
Fig.  12  will  show  that  with  the  series  motor  a  large  torque  is 
available  at  low  speeds,  the  torque  and  the  current  as  well  falling 
off  as  the  car  accelerates  and  therefore  as  the  demand  for  torque 


SI)  100         120 

Amperes 

Fig.   13. 


180       200 


decreases.  Assuming  a  concrete  example,  if  a  tractive  effort  of 
1200  lb.  per  motor  is  required  to  accelerate  a  car  the  series 
motor  of  Fig.  12  will  require  but  68  amperes  of  current  while  the 
corresponding  shunt  motor  will  draw  125  amperes.     Assuming 


MOTOR   CHARACTERISTICS.  41 

that  they  are  both  operating  on  the  same  line  the  power  demand 
in  the  latter  case  will  be  nearly  double  that  of  the  series  motor. 

For  the  above  reasons  the  series  direct  current  motor  has  come 
into  almost  universal  use  for  traction  service.  During  the  last 
few  years,  however,  the  single  phase  series  motor,  with  practically 
the  same  characteristics  as  the  direct  current  series  motor,  has 
been  installed  in  a  number  of  instances.  In  several  cases  in 
Europe  and  in  one  instance  in  this  country  the  polyphase  induc- 
tion motor  has  been  adopted  where  conditions  seemed  to  be 
particularly  favorable  for  constant  speed  operation. 

Confining  the  discussion  to  series  motors,  the  characteristics 
already  considered  are  the  torque  and  speed  curves  plotted  in 
terms  of  current  input.  To  these  should  be  added  the  curves  of 
efficiency,  often  plotted  both  with  and  without  gears,  temperature 
rise,  and,  in  the  case  of  alternating  current  motors,  the  power 
factor.  These  characteristics,  Fig.  13,  may  be  obtained  either 
from  design  data  before  the  motor  is  built  or  by  test  after  its 
completion. 

Assuming  that  the  design  of  a  proposed  motor  has  been  tenta- 
tively made  and  its  dimensions  and  winding  data  known,  the 
speed,  torque,  and  efficiency  characteristics  may  be  found  as 
follows: 

E  =  Impressed  voltage. 
e=  Counter  electromotive  force. 
I  =  Current  in  amperes. 
T  =  Torque  at  i  ft.  radius  in  pounds. 
R,^  and  Rf  =  Resistance  armature  and  field  respectively. 
V  =  Speed  in  revolutions  per  minute. 
Na= Total  conductors  on  surface  of  armature. 
Nf  =  Turns  on  one  field  pole. 
</)  =  Flux  per  pole  in  Maxwells. 
p  =  Number  of  poles. 

b  =  Number  of  paths  in  parallel  on  armature. 
A  =  Area  cross  section  magnetic  circuit  at  air  gap. 
1  =  Length  magnetic  circuit. 
,«=  Equivalent  permeability  magnetic  circuit. 
W= Power  delivered  to  the  shaft  of  motor  expressed  in 
watts. 


42  ELECTRIC    RAILWAY    ENGINEERING. 

From  the  experimental  definition  of  the  volt: 

^     60  X  io«  b  ^'^ 

60  X  10*  be 
Na0p 
but  if  leakage  and  armature  reaction  be  neglected, 

Simplified 


4  TrNfIA// 


but 
therefore 


47 . 7  X  10^  bel 

N^pNfIA«  ^^^ 

e  =  E-I(R,+  R,)  (5) 

47-7xio^bl[E-I(R,+  Rf)]  . 

N,pNfIA,«  ^  ^ 


As  all  factors  in  the  right  hand  side  of  equation  (6)  are  either 
constants  of  the  design  or  dependent  upon  current,  a  series  of 
assumed  values  of  current  will  give  corresponding  values  of  speed 
(V)  from  which  the  speed  characteristic  may  be  plotted.  It  will 
be  seen  from  equation  (2)  that  if  (0)  be  constant  because  of  field 
saturation,  the  speed  (V)  will  vary  directly  with  the  counter 
e.  m.  f.  (e).  Since,  however,  the  voltage  drop  due  to  resistance  is 
a  small  percentage  of  the  impressed  voltage,  it  may  be  said  that 
the  speed  of  a  series  motor  varies  with  the  voltage  impressed  upon 
it  if  load  conditions  remain  the  same.  This  fact  is  of  importance 
in  the  design  of  car  control  systems. 

With  reference  to  the  torque  characteristic  and  neglecting  iron 
losses, 

W  =  el  (7) 

2  ttVT  X  746 

W  = ^  (8) 

33000 


whence 


^_        3300G  em^cjip 

2  -  X  746  X  60  X  10^  be 


MOTOR    CH.AR,\CTERISTICS. 


43 


or 


T 


o.  117  IN^cf^p 
10'  b 


(10) 


If  the  flux  {(f))  be  assumed  constant,  which  would  be  the  case  with 
the  magnetic  circuit  saturated,  equation  (10)  proves  that  the 
torque  of  a  series  motor  will  var\'  directly  with  the  current  as 
prenously  stated. 

While  the  elBciency  and  temperature  characteristics  can  be 
ver\'  closely  approximated  in  advance  by  means  of  empirical 
formulae,  it  is  usually  customary  to  determine  these  values  roughly 
by  comparison  with  other  machines  of  similar  design  which  have 
been  pre\dously  constructed  and  to  await  the  test  for  accurate 
results. 


Fig.  14. 


Several  methods  of  testing  are  available  for  the  determination 
of  all  the  characteristics  of  the  motor  when  constructed.  Three 
methods  will  be  briefly  outlined,  of  which  the  one  involving  the 
apparatus  most  available  may  be  selected. 

Prony  Brake  Method. — This  method  is  probably  the  simplest 
of  the  three  and  may  be  used  where  plenty  of  power  is  available 
for  the  operation  of  the  motor  up  to  50  or  100  per  cent,  overloads. 
As  the  name  implies,  the  motor  is  loaded  by  means  of  a  prony 
brake  from  which  the  torque  may  be  directly  determined,  while 
the  current  and  speed  are  read  directly  by  means  of  an  ammeter 
connected  in  series  with  the  motor  at  (A),  Fig.  14,  and  a  tachom- 
eter. The  resistance  (R)  may  be  inserted,  if  necessary,  to 
maintain  constant  voltage  across  the  motor.  The  efficiency  curve 
may  be  obtained  by  making  a  series  of  calculations  from  the 


44 


ELECTRIC    RAILWAY   ENGINEERING. 


following  formula  (13)  with  varying  currents.     It  is  believed  that 
the  derivation  of  the  formula  is  self  explanatory. 
If  T'  represent  torque  at  pulley  at  i  ft.  radius. 

2  TZVT' 

Output  (h.  p.) 


Input  (h.  p.)  = 


Efficiency  = 


33000 
EI 
746 

0.142  VT' 
EI 


(II) 


(12) 


(13) 


Pumping  Back  Method. — For  this  test  two  motors,  identical 
in  design  and  construction,  are  necessary,  but  the  method  has  the 
advantage  of  a  relatively  small  power  demand  as  the  losses  alone 
are  supplied  from  outside  sources. 


Fig.   15. 

Two  motors  are  placed  in  alignment  with  shafts  end  to  end  and 
mechanically  clutched  together.  They  are  so  connected,  Fig.  15, 
that  one  machine,  acting  as  a  motor  with  a  separately  excited 
field,  drives  the  other  as  a  generator.  The  latter  has  a  series 
connected  field.  By  varying  the  field  strength  (F')  by  means  of 
the  resistance  (R)  the  current  (A')  may  be  controlled  from  no  load 
to  overload.  The  output  of  motor  No.  2,  if  the  losses  are  supplied 
from  the  external  source  (S)  is  the  product  of  the  readings  (V) 
and  (A').  This  value  of  power,  reduced  to  foot  pounds  per 
minute  and  divided  by  2-  times  the  speed  of  the  set,  determines 


MOTOR    CHARACTERISTICS.  45 

the  torque.  Speed  and  torque  plotted  against  current  in 
amperes  read  from  meter  (A')  furnish  the  two  principal  motor 
characteristics. 

In  order  to  find  the  efficiency,  for  which  a  knowledge  of  the 
losses  is  necessary,  the  assumption  is  made  that  the  combined 
iron  and  friction  losses  of  the  two  machines  are  equal.  Since  the 
I-R  loss  of  No.  2  has  been  eliminated  from  the  calculation  by  the 
fact  of  its  separate  excitation,  the  losses  represented  by  the  power 
(AV)  must  be  made  up  of  the  following: 

Friction  losses  of  both  machines. 

Iron  losses  of  both  machines. 

I-R  losses  of  both  armatures. 

I-R  losses  of  No.  i  field. 
If  the  resistances  of  both  armatures  and  fields  are  known,  the 
I-R  losses  can  be  readily  calculated  for  the  various  values  of 
current.  These  losses  subtracted  from  (AV)  leave  the  total 
iron  and  friction  losses  of  the  two  machines,  one  half  of  which, 
according  to  the  above  assumption,  is  chargeable  to  each  motor. 
Thus  the  losses  and  therefore  the  efficiency  of  the  motor  under 
test  become  known  and  the  efliciency  characteristic  may  be 
plotted.  If  a  more  detailed  analysis  of  iron  and  friction  losses  is 
desired,  additional  tests  with  dififerent  connections  must  be  made.^ 

The  two  temperature  curves  of  Fig.  13  showing  respectively 
the  time  required  for  the  motor  to  rise  75°  C.  above  the  room 
temperature  when  starting  cold  and  the  time  to  rise  20°  C.  above 
the  temperature  of  75°  C.  for  the  various  currents  in  the  motor 
circuit,  are  of  the  greatest  value  in  selecting  the  proper  motor 
for  a  given  service  not  only,  but  for  determining  the  tempera- 
ture rise  corresponding  to  various  overloads  which  the  motor  will 
usually  be  called  upon  to  carry  for  short  intervals  of  time.  The 
values  from  which  these  curves  may  be  plotted  can  best  be  ob- 
tained by  actual  test  preferably  with  the  connections  of  Fig.  15, 
separate  runs  being  made,  of  course,  for  each  value  of  current. 
Thermometers  placed  on  the  various  parts  of  the  machine  during 
the  run  indicate  when  the  desired  temperature  has  been  reached 
and  the  time  for  such  rise  may  then  be  plotted  against  the  con- 
stant value  of  current  maintained  during  the  test.     Additional 

*  See  "Experimental  Electrical  Engineering"  by  V.  Karapetoff,  pp.  406-407. 


46  ELECTRIC    RAILWAY    ENGINEERING. 

thermometers  may  be  applied  to  determine  the  temperature  of 
rotating  parts  at  the  end  of  the  test  and  the  hot  resistance  of  the 
windings  taken  to  determine  by  calculation  tRe  internal  tempera- 
tures of  the  coils. 

Motor  Used  as  a  Generator. — In  this  case  the  motors  are 
mechanically  clutched  together  as  in  the  "pumping  back"  test, 
one  being  used  as  a  motor  to  drive  the  other  as  a  generator.  The 
latter  is  loaded  by  means  of  a  water  rheostat  as  shown  in  Fig.  i6. 
The  calculations  for  losses  and  efficiency  are  very  similar  to  those 


Fig.   i6. 

in  the  pre\ious  test,  this  method  differing  from  the  former  prin- 
cipally in  the  type  of  load  used.  These  connections  are  often 
used  by  the  manufacturing  companies  for  the  one-hour  heat  run 
usually  applied  to  railway  motors. 

Gear  Ratio. — Since  a  suitable  design  for  a  railway  motor  de- 
mands a  speed  much  higher  than  that  at  which  the  car  axle  should 
be  driven  in  ordinary  installations,  single  reduction  gearing  is 
introduced  between  the  motor  shaft  and  the  car  axle,  a  pinion 
upon  the  former  engaging  a  gear  keyed  to  the  latter. 

It  has  become  customary  in  railway  practice  to  express  this 
gear  ratio  as  an  integer,  or 

No.  teeth  in  gear 
Gear  Ratio  =  — — r^iT r       ..  (14) 

No.  teeth  in  pinion 

As  it  is  most  convenient  to  plot  the  characteristic  curves  of 
railway  motors  in  terms  of  forces  at  the  periphery  of  the  car  wheel 
and  speeds  in  miles  per  hour  travelled  by  the  car,  it  is  obvious 
that  a  given  group  of  such  curves  is  dependent  upon  a  single 
definite  car  wheel  diameter  and  gear  ratio.  With  a  change  of 
gear  ratio,  however,  the  motor  speed  remaining  the  same,  the 
speed  of  the  car  will  change  in  the  inverse  proportion  while  the 


MOTOR    CHLARACTERISTICS.  47 

tractive  effort  will,  of  course,  vary  in  direct  proportion  to  the 
change  in  gear  ratio. 

The  torque  and  speed  characteristics  may,  therefore,  be  changed 
to  apply  to  a  new  gear  ratio  by  the  use  of  the  proportions  gi\en 
in  equations  (15)  and  (16). 

New  Speed  Old  gear  ratio 

Old  speed  New  gear  ratio 

New  tractive  effort  New  gear  ratio 

Old  tractive  effort  Old  gear  ratio 

Motor  characteristics  thus  changed  are  represented  by  the 
dotted  lines'of  Fig.  i^. 


CHAPTER  VI. 

Speed  Tbie  Curates  (Components.) 

Weight  of  Car. — From  the  familiar  relation  Force  =  Mass  x 
Acceleration  expressed  in  the  formula: 

F  =  ma  (17) 

it  is  clear  that  the  weight  of  the  car,  complete  with  its  equipment 
and  load,  will  enter  into  the  calculations  for  the  speed  time  curve 
as  an  important  factor.  The  above  equation  may,  however,  be 
reduced  to  a  form  more  convenient  for  railway  application  as 
follows : 

m  =  w/g  (18) 

where  (w)  represents  the  weight  in  pounds  and  (g)  the  accelera- 
tion of  gra\ity  (32.2).  Equation  (17)  becomes  with  this  substi- 
tution 

wa  ,     ^ 

F=    --  (19) 

32.2 

Changing  to  the  more  convenient  units  of  miles  per  hour  in  place 

5200 
of  feet  per  second  by  means  of  the  constant  i  m.  p.  h.  =  \     = 
^  3600 

1.467  ft.  per  sec.  or  (a)  =  1.467  A,  when  (A)  is  expressed  in  miles 
per  hour  per  second  and  substituting  2000  W  in  place  of  (w) 
expressed  in  pounds  equation  (19)  becomes 

WAx  2000  X  1.467 

F= =9i.iWA  (20) 

32.2 

In  order,  therefore,  to  accelerate  a  car  at  a  rate  of  i  m.  p.  h. 
p.  s.,  a  net  force  of  91. i  lb.  must  be  exerted  for  every  ton  weight 
of  car.  It  must  be  remembered  that  this  net  force  available 
for  acceleration  is  only  that  which  remains  after  all  frictional 
resistances  of  the  car  have  been  overcome. 

It  is  now  possible  to  obtain  a  relation  between  the  tractive  effort 
of  the  motors  comprising  the  car  equipment  and  the  acceleration 

48 


SPEED    TIME    CURVES.  49 

that  this  tractive  effort  will  produce  for  a  given  weight  of  car. 
This  will  ob\iously  depend  upon  whether  a  two  or  four  motor 
equipment  is  used.     Equation  (20)  may  be  written 

if  n  =  Number  of  motors  on  car 
Pj^  =Net  tractive  effort  per  motor. 

From  the  above  equation  it  will  be  seen  that  the  acceleration  is 
inversely  proportional  to  weight  of  car. 

Bearing  and  Rolling  Friction. — In  studying  the  various 
retarding  forces  which  have  to  be  overcome  by  the  motors  in  car 
operation  and  which  must,  therefore,  be  subtracted  from  the 
gross  tractive  effort  of  the  motors  in  order  to  determine  the  net 
effort  available  for  acceleration,  it  seems  logical  to  consider  first 
those  forces  acting  under  the  normal  conditions  of  a  straight  level 
track.  Among  these  forces  are  found  the  friction  of  armature 
and  axle  bearings.  The  axle  friction,  which  is  usually  the  greater 
of  the  two,  varies  with  the  pressure  on  the  bearing,  and  therefore 
with  the  weight  of  the  car  for  a  given  truck  arrangement.  Both 
frictional  resistances  vary  very  nearly  in  proportion  with  the 
speed.  In  building  up  an  empirical  formula  for  train  resistance, 
therefore,  expressed  in  pounds  train  resistance  per  ton  weight  of 
car,  it  would  be  expected  that  bearing  friction  would  be  represented 
therein  by  a  constant  term  added  to  a  term  varying  with  speed. 

There  are  found  to  be  present,  however,  in  the  operation  of  a 
car  other  frictional  forces  exerted  between  the  wheels  and  rails. 
These  forces  have  been  termed  "rolling  friction."  They  are 
caused  partly  by  the  rubbing  of  the  wheel  flange  against  the  head 
of  the  rail  and  partly  by  the  fact  that  there  is  apparently  a  slight 
depression  in  the  rail  under  each  wheel  out  of  which  the  wheel 
must  be  forced  against  an  appreciable  resistance.  This  effect  is 
more  marked  with  a  greater  distance  between  ties  or  in  cases 
where  rail  spikes  have  become  loosened,  allowing  considerable 
vertical  motion  to  the  rail  as  the  car  passes  over  it.  Since  the 
flange  friction  previously  mentioned  is  considerably  increased  if 
the  track  gauge  is  not  maintained  constant,  the  entire  item  of  roll- 
ing friction  may  vary  greatly  with  the  condition  of  the  track.  As 
4 


5©  ELECTRIC    RAILWAY    ENGINEERING. 

this  resistance  will  also  vary  with  the  speed  and  weight  of  the  car 
for  a  given  track,  both  bearing  and  rolling  friction  may  be  repre- 
sented by  a  single  constant  plus  a  second  term  varying  with  speed. 

Air  Resistance. — The  amount  of  resistance  offered  to  the 
motion  of  the  car  by  the  air  is  very  surprising,  especially  in  the 
case  of  single  cars  at  relatively  high  speeds.  Not  only  is  there 
considerable  resistance  offered  to  the  front  cross  section  of  the 
car  as  it  cuts  through  the  various  strata  of  air  but  the  friction  of  the 
air  upon  the  sides  of  the  cai  and  the  eddies  and  suction  produced 
at  the  rear  cause  a  considerable  retarding  effect  upon  the  motion 
of  a  train.  This  suction  phenomenon  may  readily  be  observed 
at  the  rear  of  a  high  speed  train  by  noting  the  motion  which  it 
conveys  to  cinders  and  light  objects  found  along  the  track. 

This  air  friction  upon  the  various  portions  of  the  car  has  been 
more  or  less  successfully  measured  in  train  resistance  tests, 
but  there  still  exists  a  wide  difference  of  opinion  regarding  its 
absolute  value.  It  is  generally  conceded,  however,  that  the 
front  and  rear  end  resistances  are  proportional  to  the  cross-sec- 
tional area  of  the  car  from  car  axle  to  roof  and  that  the  side  resist- 
ance of  a  single  car  is  approximately  one-tenth  of  the  sum  of  head 
and  rear  resistances.  Since  the  side  resistance  is  much  smaller 
than  the  end  resistance  it  would  be  expected  that  the  total  air 
resistance  per  ton  weight  of  car  would  be  very  much  greater  for  a 
single  car  than  for  a  train.  This  has  been  found  to  be  so  marked 
in  the  tests  carried  out  that  it  is  usually  impractical  to  operate  a 
single  car  much  over  60  m.  p.  h.,  while  a  train  of  many  cars 
may  be  operated  at  much  higher  speeds  without  serious  loss. 
While  this  air  resistance  is  a  comparatively  small  quantity  at  low 
speeds,  it  is  generally  considered  to  vary  with  the  square  of  the 
speed  and  is  therefore  a  very  formidable  factor  at  high  speeds. 

As  a  result  of  the  various  train  resistance  tests  which  have  been 
made  by  determining  the  deceleration  of  cars  and  trains  while 
coasting  from  different  initial  speeds  to  a  standstill  on  a  straight 
level  track,  a  number  of  empirical  formulas  have  been  suggested 
and  used  with  varying  degrees  of  accuracy  in  train  calculations. 
The  tests  which  have  been  made  comparatively  recently  with 
electric  equipment,  with  which  the  power  is  much  more  accurately 
measured  than  in  steam  locomotive  tests,  may  be  represented  by 


SPEED    TIME    CURVES. 


51 


the  curves  of  Fig.  17,  plotted  in  pounds  per  ton  train  resistance 
for  25  ton  cars  against  speed  in  miles  per  hour.  This  train 
resistance  includes  bearing  and  rolling  friction  and  air  resistance 
upon  the  entire  car  or  train. 


90 
85 
80 
75 

70 
Oo 
00 

5^55 
^5  50 

1^5 

i.40 
m 

a5 
20 

15 
10 


TRAIN  RESISTANCE  CURVES. 

25  TON  CAR  WITH  VARYING  SPEED 

^^ 

/ 

/ 

/ 

^ 

^ 

< 

«3 

f 

V 

/ 

/• 

y 

/ 

f 

y 

0.$^ 

y 

/ 

/ 

y 

/ 

/ 

> 

/ 

/ 

y 

/ 

\ 

c^ 

^ 

/ 

f 

/ 

/ 

/ 

^ 

y 

/ 

/ 

/ 

y 

^ 

/ 

f 

V 

/ 

y 

/ 

/ 

/ 

/ 

f 

/ 

/ 

', 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

I 

// 

J 

/ 

1 

7 

/ 

;/ 

/ 

/ 

/ 

1 

/ 

\'\\ 

f 

! 

10  15  :io  25  30  aj 

Train  Itesistaiiee  in  Lbs.  per  Ton 

Fig.    17. 


40 


The  empirical  formula  from  which  these  curves  were  plotted 
and  which  probably  approximates  most  closely  the  true  train 
resistance  in  practice  is  represented  below. 


50  .002    -•  /       n  — : 


(22) 


R  =  Total  train  resistance  in  pounds  per  ton  weight  of  train. 
W  =  Weight  of  train  in  tons. 
V=:  Speed  of  train  in  miles  per  hour, 
a  =  Area  of  cross  section  of  front  end  of  car  or  locomotive 

above  axle  expressed  in  square  feet. 
n  =  Number  of  cars  in  train. 


'  See  "Electric  Traction"  bv  A.  IT.  Armstronj: 


52 


ELECTRIC    RAILWAY    ENGINEERING. 


In  this  formula  the  first  two  terms  express  the  rolling  and  bear- 
ing friction  while  the  last  term  determines  the  resistance  due  to  air 
friction  and  suction. 

The  effect  of  increased  weight  of  cars  upon  train  resistance  at 
constant  speed  is  very  clearly  shown  in  the  curves  of  Fig.  i8, 
which  are  plotted  from  the  same  formula.  It  must  be  remem- 
bered that  this  effect  is  entirely  separate  from  the  extra  tractive 


60 


TRAIN  RESISTANCE  CURVES. 

SINGLE  CAR  OF  VARYING  WEIGHT 

AT  CONSTANT  SPEED. 


10  15  ao  25  30  35 

Resistance  in  Lbs.  per  Ton 

Fig.  i8. 


40 


effort  necessary  to  accelerate  the  heavier  cars  and  therefore 
represents  an  additional  negative  force  or  resistance  which  the 
motors  are  called  upon  to  overcome  when  operating  hea\y  rolling 
stock. 

Rotative  Inertia  of  Wheels  and  Armature. — It  will  be 
remembered  from  mechanics  that  if  two  dift'erent  rotating  masses 
of  different  inertia  are  acted  upon  by  similar  propelling  and  simi- 
lar resisting  forces  respectively,  the  mass  having  the  greater  in- 


SPEED   TIME   CURVES.  53 

ertia  will  have  the  lower  value  of  acceleration  or  decleration  as 
the  case  may  be. 

From  this  fact  it  would  be  expected  that  the  relatively  large 
inertia  of  the  rotating  elements  of  the  car,  including  motor  arma- 
tures, gears,  pinions,  axles,  and  wheels  would  tend  to  reduce  the 
acceleration  when  the  car  is  starting  and  the  deceleration  when 
coasting  and  braking.  This  inertia  factor  must  be  taken  into 
consideration  in  the  accurate  calculation  of  speed  time  curves  as 
follows : 

The  energy  of  rotation— 

0,^1     M^^k^  ,     ^ 

E=       = (23) 

2  2 

since  I  =  Mk^  (24) 

where  w  =  Angular  velocity, 

I  =  Moment  of  inertia, 

M  =  Mass, 

k  =  Radius  of  gyration. 

These  fundamental  formulae  will  be  applied  to  this  particular 

problem  with  the  following  nomenclature : 

n^  =  Number  of  pairs  of  wheels  on  car. 

n^^  Number  of  armatures  on  car. 

W^  =  Weight  of  each  pair  of  wheels  and  axle  in  tons. 

Wa  =  Weight  of  each  armature  in  tons. 

k^  =  Radius  of  gyration  of  wheels  and  axle. 

ka  =  Radius  of  gyration  of  armature. 

r=  Radius  of  wheels  in  feet. 

A  =  Acceleration  of  car  in  m.  p.  h.  /sec. 

V  =  Velocity  of  car  in  m.  p.  h. 

v= Velocity  at  extremity  of  radius  of  gyration. 

g  =  Acceleration  of  gravity. 

G  =  Gear  ratio. 

W  =  Weight  of  car  in  tons. 

p  =  Net  tractive  effort  at  periphery  of  wheel. 

Considering  first  the  wheels  and  axles: 

From  equation  (23) 

K=  (25) 

2g 


54  ELECTRIC    RAILWAY   ENGINEERING. 

But 

k^w-v  (26) 

Substituting 

^w  =  n,      ,,-  (27) 

Since  the  velocity  of  the  periphery  of  the  car  wheel  is  the  same 
as  that  of  the  car,  if  it  be  assumed  that  no  slipping  occurs, 

W   /k     V 
E,  =  n,--(-;v)  (.8) 

or,   in   other  words,  replace   n^W^  with  the  equivalent  weight 

KV 
^  J  n^W^if  (V)  is  used  in  (27). 

In  a  similar  manner,  remembering  that  in  transferring  armature 
values  to  those  at  the  periphery  of  the  wheel  the  gear  ratio  (G) 
must  be  introduced, 

/K   Y- 

from  which  the  equ.valent  weight  isl      G  I  n^W^^ 

By  adding  the  new  values  of  equivalent  weight,  expressed  in 
tons,  necessary  to  overcome  rotational  inertia,  therefore,  formula 
(20)  may  be  corrected  to  read 


F  =  9i.i  A 
Since  the  radius  of  gyration 


k  \  2  /k  G\  2' 

W+n^WJ  ;']   +n,Wj  ^ 


(30) 


and  all  revolving  parts  to  be  considered  in  electric  traction  are 
cyl'nders  revohing  about  their  axes, 

I  =  m'  (32) 

2 

k=    /-  (33) 

V2 


SPEED    TIME    CURVES. 


D^) 


In  order  to  determine  approximately  the  magnitude  of  the 
inertia  of  rotating  parts  the  following  concrete  values,  which  are 
often  found  in  practice  may  be  assumed. 


nw  =  n^ 

=  4 

W^=i5oo  lb. 

=  0.75  ton 

W^=7oolb. 

=  0.35  ton 

33  in. 
r  = 

2  X  12 

=  1-375  ft. 

,           33  in. 

K= /- 

2  X   I2\/2 

=  0.97  ft. 

^4"!. 

^        2  X  I2\/'2 

=  0.412  ft, 

A=i  m.  p.  h. 

/sec. 

0  =  19/52  =2.74 

W  =  25  tons. 
Substituting  in  (30) 

F  =  9i.i  (25+1.49+ .944)  =  2500  lb. 

or  100  \]).  per  ton.  In  other  words,  the  net  tractive  effort 
necessary  for  translation  must  be  increased  approximately  9.8 
per  cent,  for  this  car  in  order  to  overcome  the  inertia  of  rotating 
parts  for  an  acceleration  of  i  m.  p.  h.  /sec. 

For  approximate  calculations,  100  lb.  per  ton  is  often  as- 
sumed for  the  net  tractive  effort  without  calculation  of  rotative 
inertia.  The  following  table  taken  from  the  Standard  Handbook 
will  give  other  values  which  may  be  assumed  under  varying 
conditions. 

TABLE  V. 
Per  Cent,  of  Total  Tr.\ctive  Effort  Consumed  in  Rot.\ting  Parts. 

Electric  locomotive  and  heavy  freight  train 5  per  cent. 

Electric  locomotive  and  high  speed  j)assenger  train 7  per  cent. 

Electric  high  speed  motor  cars 7  per  cent. 

Electric  low  speed  motor  cars • 10  per  cent. 

Grades. — Whenever  a  grade  is  encountered  it  is  not  only 
necessary  to  provide  an  additional  tractive  effort  to  overcome 


56 


ELECTRIC    RAILWAY   ENGINEERING. 


linear  and  rotational  inertia,  but  it  is  also  necessary  to  make  use 
of  some  of  the  tractive  effort  of  the  motors  in  actually  lifting  the 
car  through  the  vertical  distance  represented  by  the  grade.  In 
other  words,  referring  to  Fig.  19,  the  weight  of  the  car  (W)  may 
be  resolved  into  the  two  forces  (N)  and  (W  sin  a)  which  are 


Fig.  19. 

normal  and  parallel  to  the  track  respectively.  The  reaction  of 
the  track  balances  the  former  while  a  force  proportional  to  the 
latter  must  be  supplied  by  the  motors  of  the  car.  As  the  angles 
(a)  and  {a')  are  equal  it  is  ob\dous  that  this  force  is  proportional 
to  the  grade  and  amounts  to  o.oi  x  2000=20  lb.  per  ton  weight 
of  car  for  each  per  cent,  of  grade.     If  the  car  is  on  a  down  grade 


this  force  is  available  for  producing  acceleration  and  is  therefore 
added  to  the  tractive  effort  of  the  motors. 

Curves. — Before  it  is  possible  to  consider  the  resistance  offered 
to  the  passage  of  a  car  or  train  by  curves  in  the  track,  it  is  neces- 
sary to  understand  clearly  the  method  of  rating  curves.  In  city 
streets  where  sharp  curves  are  met  with,  they  are  usually  desig- 


SPEED   TIME   CURVES.  57 

nated  by  their  radii,  e.g.,  a  curve  of  30  ft.  radius.  On  private 
rights  of  way,  however,  in  suburban  and  interurban  construction 
it  has  been  customary  to  designate  curves  in  degrees  of  central 
angle  subtended  by  a  chord  of  100  ft.  Referring  to  Fig.  20,  if 
angle  (^)  is  drawn  so  that  it  is  subtended  by  the  chord  (ac)  of 
100  ft.  and  (0)  =  i°,  then  the  radius  (Ob)  necessary  to  make 
this  assumption  correct  is  found  as  follows: 

50 
tan  30'=  .0087- .^"  or  (Ob)  =  5730  ft. 

The  radius  of  a  1°  curve  is  therefore  5730  ft. 
If  now  (ab)  be  moved  toward  (O)  such  a  distance  as  to  make 
(Oe)  =  (eb) 

0        50 
tan    -  =  ;^^   =  .oi7t;  =  tan  1°  or  ^  =2°. 
2      2865  '^ 

5730 
Therefore,  curvature  in  degrees  =      ,. 

radius 

As  a  car  enters  a  curve  there  is,  of  course,  a  tendency  to  ride 
over  the  outer  rail  and  there  occurs  between  the  flange  of  the  car 
wheel  and  the  head  of  the  rail  considerable  frictional  force 
tending  to  cause  the  car  to  follow  the  rail  but  at  the  same 
time  retarding  the  motion  of  the  car.  This  force  must  be 
considered  as  an  additional  resistance  which  manifests  itself  in 
frictional  heat. 

The  amount  of  this  resistance  has  been  approximated  from 
test  data  and  it  is  conceded  that  it  is  directly  proportional  to  the 
curvature  in  degrees.  Values  ranging  from  0.52  lb.  to  i  lb.  per 
ton  weight  of  car  per  degree  curvature  have  been  obtained  but 
good  practice  at  present  stipulates  0.6  lb.  per  ton  weight  of  car 
per  degree  curvature.  When  the  car  is  on  a  curve,  therefore,  an 
additional  force  of  o .  6  W  x  degrees  curvature  must  be  subtracted 
from  the  gross  tractive  effort  in  addition  to  all  resistances  pre- 
viously considered. 

Probably  the  best  method  of  summarizing  the  discussion  of 
train  resistance  is  to  express  in  terms  of  a  formula  the  derivation 


58  ELECTRIC    RAILWAY    ENGINEERING. 

of  the  net  tractive   effort  available   for  acceleration   from  the 
gross  tractive  effort  obtained  from  the  motors,  thus — 

p  =  P-f±g-c  (35) 

where 

P  =  Gross  tractive  effort  of  motors  in  pounds  per  ton. 

p  =  Net  tractive  effort  available  for  acceleration  in  pounds 

per  ton. 
f  =  Train  resistance  due  to  bearing  and  rolling  friction  and 

air  resistance  in  pounds  per  ton. 
g=  Resistance  due  to  grades  in  pounds  per  ton. 
c  =  Resistance  due  to  curves  in  pounds  per  ton. 

The  use  of  this  net  tractive  effort  (p)  in  calculating  the  acceler- 
ration  of  a  car  or  train  will  be  discussed  in  detail  in  the  following 
chapter. 


CHAPTER  \  II. 
Speed  Time  Curves  (Theory). 

Having  considered  in  detail  the  various  factors  entering  into 
the  speed  time  curve,  the  methods  of  plotting  same  may  now  be 
considered.  Two  methods  are  in  general  use,  the  so-called  "cut 
and  try"  method  which  involves  considerably  more  time  for  its 
performance  but  which  is  the  more  accurate,  and  the  "straight 
line"  method  which  assumes  all  portions  of  the  diagram  made 
up  of  straight  lines,  thereby  simplifying  the  calculation  at  the 
expense  of  the  introduction  of  slight  errors.  The  former  and 
more  accurate  method  will  first  be  considered,  for  only  through 
the  complete  analysis  of  the  correct  curves  can  a  thorough 
understanding  of  electric  car  performance  be  obtained. 

The  distance  between  the  two  consecutive  stops  having  been 
determined,  it  is  next  necessary  to  select  the  proper  schedule  speed 
for  the  run,  i.e.,  the  average  speed,  which  if  maintained  constant 
throughout  the  run  would  bring  the  car  to  its  destination  in  the 
required  time.  This  speed  is  usually  determined  from  traffic 
studies,  and  is,  of  course,  dependent  upon  the  train  schedule  of 
the  entire  system.  With  the  distance  and  schedule  speed  deter- 
mined, the  time  required  for  the  run  can  be  calculated  and  the 
limits  of  the  curve  laid  off  graphically  to  scale  as  (OT)  in 
Fig.  21. 

The  nomenclature  which  will  be  used  is  as  follows: 

T.E.  =  Gross  tractive  effort  per  motor  in  pounds. 

P  =  Gross  tractive  effort  at  periphery  of  car  wheel  in 

pounds  per  ton. 
p  =  Net  tractive  effort  in  pounds  per  ton. 
v  =  Speed  corresponding  to  (TE)  in  m.  p.  h. 
I  =  Current  corresponding  to  (TE)  in  amperes. 
A  =  Acceleration  in  m.  p.  h./sec. 
D  =  Deceleration  in  m.  p.  h./sec 

59 


6o 


ELECTRIC    RAILWAY    ENGINEERING. 


V  =  Schedule  speed  in  m.  p.  h. 

S  =  Length  of  run  in  feet. 
s  s',  etc.    =  Distances  in  feet. 

T  =  Time  for  entire  run  in  seconds. 
1,1',  etc.,    =Time  for  portions  of  run  in  seconds. 

f  =  Train  resistance  in  pounds  per  ton. 

g  =  Grade  resistance  in  pounds  per  ton. 


40 

SPEED  AND  DISTANCE  CURVES. 

^ 

^ 

y 

^ 

/' 

, 

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" 

^ 

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30 

^ 

^ 

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500 


0   10   20  30  ■  40   50  (iO  70   SO   00  100  110  120  130  140  150  KiO  170  180  100  200 

Fig.  2  1. 


c  =  Curve  resistance  in  pounds  per  ton. 

b  =  Braking  resistance  in  pounds  per  ton. 

W=  Weight  of  car  in  tons. 

n  =  Number  of  motors  on  car. 

Wj  =  Weight  of  car  per  motor  in  tons. 

Referring  t6  Fig.  21. 

S 

OT  =  T  =  - (36) 

Vx  1.467  ^^  ' 

The  acceleration   (A)  must  be  assumed  sufficiently  large  to 


SPEED    TIME    CURVES.  6 1 

enable  the  desired  schedule  to  be  made  and  yet  not  so  great  as 
to  be  of  inconvenience  to  passengers.     The  method  of  calculating 
the  net  tractive  effort  (p)  has  been  previously  explained  in  formulae 
and  it  will  therefore  be  considered  as  a  known  quantity. 
The  gross  tractive  effort  per  ton  may  now  be  found 

P=(p  +  f±g  +  c)  (37) 

The  sign  of  the  grade  resistance  (g)  depends,  of  course,  upon 
whether  the  car  is  ascending  or  descending  the  grade;  in  the 
latter  case  the  sign  is  negative  and  the  gross  tractive  effort 
necessary  is  decreased  by  the  presence  of  the  grade. 

The  weight  of  car  which  must  be  accelerated  by  each  motor  is : 

W 

The  gross  tractive  effort  which  the  motor  must  exert  is  therefore : 

W 

T.E.=PW,=^^(p+f±g+c)  (39) 

Referring  to  the  characteristic  curves  of  the  motor  which  has 
been  assumed  as  probably  of  the  correct  design  for  this  service 
the  gross  tractive  effort  (T.E.)  is  found  to  correspond  to  a  current 
I  (Oa,  Fig.  22)  and  at  this  current  the  speed  is  v  (ab,  Fig.  22). 
The  motors  of  the  car  will  be  able  to  nii^intain  this  rate  of  acceler- 
ation (A)  as  long  as  they  can  be  supplied  with  current  I  =  Oa. 
As  the  speed  increases,  however,  the  current  and  therefore  the 
tractive  effort  will  decrease  unless  the  voltage  applied  to  the  motors 
is  increased.  This  is  the  function  of  the  control  equipment 
whether  it  be  of  the  rheostatic,  series  parallel,  or  auto-transformer 
type.  Until  such  time  as  the  voltage  impressed  upon  the  motors 
reaches  the  maximum  value  possible  with  the  particular  control 
equipment  in  use  the  assumed  value  of  acceleration  (A)  may  be 
used  for  calculation.  In  other  words  the  acceleration  portion  of 
the  speed-time  curve  may  be  drawn  as  a  straight  line  from  O'  with 

/dv  .      \        , 
a  slope  of  I       =A1  until  a  speed  is  reached  corresponding  to 

(v  =  ab),Fig.  22.     This  line  is  drawn  as  Ob'  in  Fig.  21  where 
a'b'  =  ab,  Fig.  22. 

Beyond  the  point  (b')  the  "cut  and  try"  method  using  incrc- 


62 


ELECTRIC    RAILWAY   ENGINEERING. 


ments  of  speed  and  time  must  be  used.     The  time,  t  =  Oa'  corre- 
sponding to  point  b',  can  readily  be  calculated  from  the  equation 


V    a'b' 


(40) 


Assuming  a  small  increment  of  speed  beyond  point  (b')  =  dv, 
the  new  speed  is  (v  +  dv)=ec.     Referring  to  the  characteristic 


30 


25 


20 


X 


10 


SPEED  AND  TORQUE  CHARACTERISTICS 
OF  WESTINGHOUSE  "  56  MOTOR 


\ 

\ 

\ 

V 

N 

\ 

\ 

-f^h 

1 

^<if 

1 
1 
1 

"■^^ 

"SSs" 

1 
1 
1 

1 

* 

1 
1 

iy^ 

1 
1 
1 

.•S0^> 

r>^>^ 

1 

\e 

IT 

H 
4000 

3500 

3000 

2500 

2000 

1500 

1000 

500 


20   40   60   80   100   120   140   160   180  200 
Amperes 

Fig.  22.     • 


curves  (Fig.  22),  this  speed  (ec)  corresponds  to  a  gross  tractive 
effort  T.E.''  =  (ef).  It  is  now  necessary  to  determine  what  accel- 
eration this  tractive  effort  can  produce  as  follows: 

T.E.' 
Net  tractive  effort      P' =    -^    -f'±g'-c'  (41) 


SPEED    TIME    CURVES.  63 

If  the  speed  increments  are  selected  sufficiently  small  the 
value  of  (f)  will  not  be  materially  different  from  (f ) ,  although  for 
accurate  work  substitution  should  be  made  of  the  resistance  from 
the  train  resistance  curves,  Fig.  17,  for  the  average  speed  repre- 
sented by  the  increment  (dv).  The  distance  curve  explained 
below  will  determine  the  portions  of  track  corresponding  to 
various  points  on  the  speed  time  curve,  thus  permitting  correct 
values  of  (g)  and  (c)  to  be  selected.  In  many  cases  these  latter 
values  do  not  change  materially  throughout  the  calculation. 

Having  determined  the  new  value  of  net  tractive  effort  (p') 

p' 
A'  =  — A  (42) 

P 

where  (A')  is  the  new  acceleration  for  the  increment  of  speed  (dv). 

The  time  required  to  traverse  the  distance  (ds)  may  be  calculated 

from  the  equation 

dv 
dt=^,  (43) 

The  coordinates  of  the  next  point  upon  the  acceleration  curve 
are  therefore  known  to  be  (v+dv)  =g'b"  and  (t  +  dt)  =0g'  and 
the  point  may  therefore  be  plotted  as  (b"). 

If  this  procedure  be  continued,  assuming  new  increments  of 
speed  and  calculating  the  corresponding  values  of  the  time 
increments,  the  complete  acceleration  curve  may  be  plotted. 
This  curve  will  become  horizontal  when  the  acceleration  reaches 
zero;  or,  in  other  words,  when  the  gross  tractive  effort  of  the 
motors  is  completely  balanced  by  the  resistances  so  that  no  net 
tractive  effort  remains  to  produce  acceleration.  With  no  change 
in  grade  or  curvature  of  track  the  car  will  continue  running  at 
constant  maximum  speed  until  the  power  is  shut  off. 

Coasting. — The  amount  of  coasting  permissible  in  a  given 
run  varies  widely.  In  some  instances  where  schedules  arc  very 
conservatively  planned  and  the  equipment  more  than  adequate 
for  the  demands  made  upon  it,  excessive  coasting  is  introduced, 
while  in  heavy  suburban  and  elevated  service,  braking  is  often 
begun  as  soon  as  power  is  shut  off,  the  coasting  portion  of  the 
curve  being  entirely  eliminated.  In  order  to  be  able  to  make  up 
time  in  case  of  delay,  however,  some  coasting  should  be  provided 


64  ELECTRIC    IL\ILWAY    ENGINEERING. 

for  in  the  speed  time  curve,  the  time  involved  in  this  portion  of 
the  run  acting  as  a  storage  reservoir  for  a  hydraulic  plant 
since  it  may  be  drawn  upon  if  necessary  to  maintain  normal 
schedules. 

In  order  to  plot  an  absolutely  accurate  coasting  curve  the 
"cut  and  try"  method  should  be  used,  since  the  average  speed 
during  the  coasting  period,  from  which  the  train  resistance  factor 
(f)  is  obtained,  is  difficult  to  predetermine  and  for  the  further 
reason  that  the  resistance  (f)  does  not  vary  directly  with  the 
decrease  in  speed.  It  is  customary,  however,  to  consider  the 
coasting  portion  of  the  diagram  as  a  straight  line,  i.e.,  to  assume 
the  deceleration  constant,  and  to  select  the  value  of  (f)  from  appro- 
priate resistance  curves  (Fig.  17)  for  an  approximate  average 
speed  during  coasting,  or  even  to  assume  (f)  directly.  This  value 
is  often  taken  arbitrarily  at  15  lb.  per  ton. 

With  the  value  of  (f)  known,  the  deceleration  is 

-(f±g  +  c) 

D^= A  (44) 

P 

from  which  the  increment  of  time  (dt)  corresponding  to  an 
assumed  change  of  speed  (dv)  may  be  calculated  as  follows: 

cit=-  (45) 

c 

The  coasting  line  may  then  be  drawn  through  (f),  Fig.  21, 

dv 
with  a  slope  D^  =       .     Such  a  line  is  (fk),  Fig.   21   (f ),  being 

any  point  arbitrarily  selected  upon  the  acceleration  curve.  The 
line  (fk)  determines  the  direction  but  not  necessarily  the  exact 
position  of  the  coasting  line. 

Braking. — Since  the  speed  time  curve  must  cut  the  time  axis 
at  T,  Fig.  21,  in  order  that  the  run  may  be  completed  in  the  pre- 
determined schedule  time,  the  braking  line  can  best  be  drawn  back 
from  T,  the  slope  being  determined  by  the  assumed  braking 
deceleration  as  in  the  case  of  the  coasting  curve.  As  in  the  case 
of  acceleration  this  rate  must  be  selected  sufficiently  high  to  enable 
the  schedule  to  be  maintained  and  yet  not  prove  disagreeable  to 
passengers.     In  heavy  suburban  and  elevated  traffic  where  speed 


SPEED    TIME    CURVES.  65 

is  relatively  high  and  headway  short  the  braking  rate  must 
necessarily  be  high.  An  average  figure  often  assumed  is  i .  5 
m.  p.  h.  /sec.    The  braking  line  in  Fig.  21  is  represented  by  Tr'. 

The  area  under  the  speed  time  curve  obviously  represents  the 
distance  travelled  during  the  run.  In  plotting  the  curve,  there- 
fore, especially  if  the  distance  time  curve  is  not  simultaneously 
plotted,  it  is  advisable  to  determine  the  area  of  the  diagram  occa- 
sionally by  means  of  a  planimeter  as  a  check  upon  the  distance. 
In  closing  the  diagram,  also,  after  the  braking  line  has  been 
drawn,  the  coasting  line  (I'm')  must  be  so  located  parallel  to  (f'k) 
that  the  area  of  the  diagram  will  correspond  to  the  distance 
travelled  between  the  stops  under  consideration.  The  completion 
of  the  diagram  is  therefore  a  "cut  and  try"  method. 

In  order  that  this  method  of  plotting  speed  time  curves  may  be 
more  clearly  understood  a  concrete  example  of  a  typical  problem 
will  be  found  in  Chapter  IX. 


CHAPTER  VIII. 

Distance,  Current,  and  Power  Time  Curves 
(Theory)  . 

The  speed  time  curve  having  been  determined,  the  secondary 
curves  which  are  dependent  thereon  may  now  be  given  consider- 
ation. 

Distance  Time  Curves. — The  distance  time  curve  which  is 
usually  plotted  simultaneously  with  the  speed  time  curve  is  also 
obtained  by  the  "step  by  step"  method,  the  series  of  increments 
of  time  determined  for  the  speed  time  curve  together  w4th  the 
corresponding  average  speeds  during  the  increment  being  used  to 
calculate  the  increments  of  distance  as  follows: 

Vj  +v, 

ds  = "   X  1.467  dt  (46) 

2 

These  increments  of  distance  when  plotted  form  the  curve 
(On'p'),  Fig.  21,  having  ordinates  expressing  distance  in  feet  cor- 
responding to  abscissae  of  time  in  seconds.  Such  a  curve  rises 
slowly  as  the  speed  increases,  maintains  a  constant  slope,  and 
gradually  approaches  the  horizontal  during  the  coasting  and 
braking  periods. 

Current  Time  Curve. — In  order  that  the  power  which  will  be 
taken  by  a  car  on  a  given  run  may  be  predetermined  the  current 
and  voltage  time  curves  must  be  plotted.  Since  the  voltage  is 
usually  assumed  constant  at  some  average  value  which  may 
reasonably  be  expected  to  obtain  over  the  entire  line  its' graphical 
representation  is  merely  a  straight  horizontal  line. 

With  the  current,  however,  it  will  be  remembered  that  the 
control  equipment  is  expected  to  maintain  practically  constant 
current  values  in  each  motor  until  the  net  tractive  effort  falls 
below  that  necessary  for  the  initial  assumed  acceleration.  This 
point,  which  is  represented  by  (b'),  Fig.  21,  has  its  time  coordi- 
nate definitely  fixed.     The  current  per  motor  (I),  as  found  from 

66 


DISTANCE,    CURRENT,    AND    POWER    TIME    CURVES. 


67 


the  characteristics  for  this  particular  speed  might  be  plotted  as 
constant  from  the  start  to  a  point  (t  =  oa').  Since,  however,  the 
series  parallel  control  is  ordinarily  used  and  the  current  con- 
sumption for  two  motors  is  the  important  consideration,  it  is 
usually  assumed  that  during  the  first  half  of  the  time  (oa'),  Fig. 
21,  the  motors  are  in  series  and  during  the  latter  half  period  in 
parallel.  The  current  consumption  for  two  motors  is,  therefore, 
double  the  value  in  the  latter  or  parallel  half  that  it  is  in  the 
first  or  series  half  of  the  constant  acceleration  portion  of  the  run. 


CURRENT  TIMECURVES 

s 

f 

< 

360 

k 

b" 



■V 

320 
2.^0 
^40 
200 

\ 

/ 

^ 

S 

K, 

\ 

\ 

/ 

s 

K 

\ 

/ 

/ 

s 

k 

0" 

/ 

iJ      ! 

9  ' 

^ 

V 

160 
120 
80 
40 

\ 

s^ 

0' 

S 

a" 

7 

^' 

10    15    20    25     30    35    40    45     50     S5    60    65     70 
Time  in  Seconds 

Fig.  2%. 


75    80    85    90    95    100 


Thus  two  of  the  motors  of  a  four  motor  equipment  would  have  a 
current-time  curve  during  the  constant  acceleration  period  rep- 
resented by  (OO'afg),  Fig.  23,  while  the  current  of  all  four  motors 
or  better,  the  current  per  car  for  the  same  period  may  be  deter- 
mined at  any  instant  from  the  curve  (00"fkb")  of  the  same 
figure.  Since  the  two  sets,  of  two  motors  each,  are  in  parallel 
with  each  other  the  total  current  per  car  in  the  series  connection 
(OO")  is  double  (00')  and  the  corresponding  "parallel"  current 
(a"b")  is  double  (OO"). 
Beyond   the   point  b",  because  of  the  increase  of  speed,  the 


68 


ELECTRIC    RAILWAY   ENGINEERING. 


current  begins  to  decrease,  each  point  on  the  curve  being  readily 
determined  by  referring  back  to  the  motor  characteristic  curve, 
Fig.  22,  for  the  current  values  corresponding  to  the  various 
coordinates  of  speed  and  time  on  the  speed  time  curve.  The 
complete  current  curve  up  to  the  time  (oq'),  Fig.  21,  where  the 
current  is  shut  off,  may  then  be  plotted  as  (00"fkb"lq'), 
Fig.  23. 

Power   Time   Curve. — The   power   taken   at   various   times 
during  the  run  can  be  very  readily  represented  graphically  with 


POWER  TIME  CURVES 
AVERAGE  VOLTAGE  500 

180 

u 

J\ 

^ 

— 

--- 

s. 

\ ' 

140 

V 

y 

^ 

S 

^v 

\ 

1, 

/ 

/ 

s 

s 

100 

\ 

/ 

/ 

s 

\ 

0" 

V 

Vj, 

I, 

^    7 

\ 

^ 

?l, 

60 

' 

20 

0, 

9 

; 

1 

1"  \ 

0  10  20  30  40  50  60  70  80  90  100 

Time  in  Seconds 

Fig.  24. 

the  same  abscissae  as  the  above  current  curve  but  with  ordinates 
which  are  the  products  of  the  current  curve  ordinates  and  the 
average  assumed  voltage.  Since  the  voltage  is  constant,  the 
power  diagram  {Of)l'i^^"\(\(),  Fig.  24,  will  take  the  same 
form  as  the  current  curve. 

If  alternating  current  series  motors  are  being  considered,  with 
which  the  series  parallel  control  is  seldom  used,  the  current  per 
motor  and  also  per  car  will  remain  fairly  constant  throughout  the 
constant  acceleration  period,  i.e.,  during  the  time  (Oa"),  Fig.  23. 
Since  the  voltage  impressed  upon  the  motors  during  this  period  is 


DISTANCE,    CURRENT,   AND    POAVER   TIME    CURVES. 


69 


usually  varied  by  means  of  an  auto-transformer  or  induction 
regulator,  neither  of  which  involve  the  power  losses  incurred  by 
the  direct  current  rheostatic  and  series  parallel  control  systems, 
the  voltage  curve  is  assumed  as  a  straight  line  betw^een  the  starting 
voltage  and  maximum  operating  secondary  voltage.  This  start- 
ing voltage,  or  the  voltage  necessary  to  produce  the  initial  tractive 
effort  may  be  determined  from  motor  tests  while  the  maximum 
operating  secondary  voltage  is  usually  that  at  which  the  motors  are 
designed  to  operate. 

If  the  product  of  the  ordinate s  of  the  current  and  voltage 
curves  for  each  of  the  time  increments  be  plotted  to  a  scale  reduced 


700 

j 

1       1       1       1 

600 

KILOVOLT  AMPERE  AND   KILOWATTTlME  CURVES 
ALTERNATING  CURRENT  SINGLE  PHASE  MOTORS 

> 

1 1 

•2  400 

1 1 

1 

V 

^300 

1 

Ov 

s 

\ 

KA 

\A. 

200 

K.W. 

100 

' 

Coast 

Brake  Sta. 
Sjtou..  Stop 

40 


80 


120 


160 


200         240         280 
Time  in  Seconds 

Fig.  2  c;. 


320        360 


400 


440 


in  the  ratio  of  1000  to  one,  a  kilovolt-ampere  curve  results  which 
is  quite  as  useful  in  determining  substation  and  distribution  sys- 
tem requirements  as  the  kilowatt-time  curve.  Fig.  25  illustrates 
such  a  kilovolt-ampere  curve  for  a  proposed  interurban  line 
operating  72  ton,  2  car  trains,  made  up  of  a  44  ton  motor  car 
and  a  24  ton  trailer  with  rotative  weight  of  4  tons,  equipped  with 
four  125  h.  p.,  200  volt,  25  cycle  single  phase  alternating  current 
series  motors  with  a  2.33  gear  ratio. 

Whereas  the  kilovolt-ampere  time  curv'e  is  of  great  value  as 
explained  above,  it  is  usually  necessary  to  know  the  actual  power 


70  ELECTRIC    RAILWAY    ENGINEERING. 

consumption  expressed  in  kilowatts  at  any  time  during  the  run. 
This  is  rendered  possible  by  plotting  the  kilowatt-time  curve, 
Fig.  25,  which  is  related  to  the  kilovolt-ampere  curve  at  any  in- 
stant by  the  expression 

Kilowatts  =  KiIovolt-amperes  x  power  factor  (47) 

Reference  to  Fig.  99,  will  show  that  the  power  factor  of  an 
alternating  current  railway  motor  varies  with  the  current.  In 
order  to  fix  accurately  a  point  on  the  kilowatt  time  curve  of  Fig. 
25,  therefore,  it  is  necessary  to  select  a  given  instant  of  time,  find 
the  current  in  the  motor  at  that  instant  from  the  current-time 
curve,  determine  the  corresponding  power  factor  from  the  motor 
characteristic  curve  and  substitute  in  equation  (47).  In  many 
cases,  however,  it  will  be  found  sufficiently  accurate  to  assume  an 
average  power  factor  for  the  entire  curve  with  the  possible  excep- 
tion of  the  starting  value  which  is  usually  considerably  lower  than 
the  average  operating  power  factor. 

The  area  enclosed  by  a  kilowatt-time  curve  is  a  measure  of  the 
energy  consumed  by  the  car  or  train  during  the  run,  thus, 

Area  of  diagram 

E  = (48) 

3000 


Ei  = -/-^^ ^-  (49) 


Area  of  diagram  x  1000x5 2 80 
3600  WS 
where 

E  =  Energy  in  kilowatt  hours. 
El  =  Energy  in  watt  hours  per  ton  mile. 
W  =  Weight  of  car  or  train  in  tons. 
S  =  Length  of  run  from  station  to  station  in  feet. 

If  this  energy  be  expressed  in  kilowatt  hours  (E)  it  will  be 
found  to  be  in  convenient  form  for  calculating  substation  demands, 
while  if  expressed  in  "watt  hours  per  ton  mile"  (Ej)  it  will  be 
found  useful  in  comparing  various  runs  with  different  types  of 
equipment  and  under  different  service  conditions,  since  it  has 
become  customary  to  express  the  results  of  power-time  curve 
calculations  for  the  purpose  of  simplicity  in  terms  of  this  unit. 


CH.\PTER  IX. 

Speed  Distance,  Current  and  Power  Curves 

(Concrete  Examples). 

In  order  that  the  use  of  the  formulae  and  the  method  of  plotting 
curves  outlined  in  the  previous  chapters  may  be  thoroughly  under- 
stood, a  typical  concrete  problem  will  be  considered.  Although 
this  particular  case  has  been  considered  because  of  its  rather 
exceptional  changes  in  grade,  involving  the  most  difhcult  phase 
of  the  problem,  the  curves  will  first  be  plotted  using  the  distances 
listed  in  Table  VI,  but  assuming  the  track  a  level  tangent.  Com- 
parative curves  will  later  be  calculated  and  plotted  to  illustrate 
the  effect  of  grades. 

table  VI.    1 
Distances  and  Gr.'^des  of  Typical  Run. 


Street  crossings.       Grade  (per  cent.)- 


Distance  from  last 

Distance   from 

stop  (feet). 

start  (feet). 

600 

600 

880 

1480 

400 

1880 

320 

2200 

1240 

3440 

760 

4200 

A  to  B. 
B  to  C. 
C  to  D. 
D  to  E. 
E  to  F. 
F   to  G. 


0.0 
6.0 

50 
2  .0 

0-5 
1 .0 


A  25  ton  intcrurban  car,  equipped  with  four  Westinghouse  No. 
56,  50  h.  p.,  d.  c.  railway  motors  and  series  parallel  control,  is 
to  be  operated  over  this  road  at  a  schedule  speed  of  18  m.  p.  h. 
The  characteristics  of  this  type  of  motor  arc  found  in  Fig.  13. 

The  initial  constant  acceleration  will  be  assumed  as  i .  25  m.  p.  h. 
p.  s.  which  is  a  fairly  representative  figure  in  electric  railway 
practice. 

71 


72  ELECTRIC    RAILWAY   ENGINEERING. 

A  force  of  loo  lb.  per  ton  will  be  considered  as  the  necessary 
tractive  effort  to  overcome  the  inertia  of  both  translation  and 
rotation  in  accelerating  the  car  at  a  rate  of  i  m.  p.  h.  p.  s. 
The  resistance  curves  found  in  Fig.  17  are  plotted  for  a  car  of  this 
weight  and  will  therefore  be  used  in  this  problem. 
*  The  values  which  must  be  substituted  for  the  symbols  listed  in 
Chapter  VII,  page  59,  are  therefore  as  follows: 

p  =  i25. 
A=i.25. 

V  =  i8. 

8  =  4200. 
W=25. 

n  =  4- 
Wi  =  6.25. 

Using  formula  (36)  the  time  of  run  is 

4200 

T= =  I SQ  seconds. 

18x1.467       ^^ 

In  order  to  substitute  in  formula  (37)  for  gross  tractive  effort 
the  value  of  train  resistance  (f)  must  be  approximated.  This  may 
be  done  sufficiently  accurately  by  selecting  the  value  from  Fig.  17 
corresponding  to  the  average  speed  which  must  be  assumed  for 
the  constant  acceleration  period. 

Taking  this  average  speed  at  10  m.  p.  h.  (f)  =  ii  lb.  per  ton. 
Froixi  equation  (37) 

P  =  (125  + 11)  =  136  lb.  per  ton. 
The  gross  tractive  effort  is  therefore : 

T.E.=6.25x  136  =  850  lb.  (39) 

Referring  to  the  characteristic  curves  of  this  motor,  Fig.  13,  the 
current  and  speed  for  this  tractive  effort  are : 
1  =  84  amp. 

V  =  20.4  m.  p.  h. 

The  average  speed  from  the  start  is  therefore  10.2  m.  p.  h. 
which  proves  the  assumption  of  10  m.  p.  h.  used  in  obtaining  the 
value  of  train  resistance  (f)  was  sufficiently  accurate.  Had  this 
assumption  been  much  in  error  a  corrected  calculation  of  tractive 
effort  should  have  been  made. 


SPEED    DISTANCE,    CURRENT  AND    POWER    CURVES.  73 

The  time  required  for  the  period  of  constant  acceleration  is 
calculated  from  formula  (40) 

20.4 
t  = =  16.3  seconds. 


I.  2 


The  line  (Ob'),  Fig.  21,  may  now  be  plotted. 
The  corresponding  distance  covered  is 

20.4 
s  =  0+  X  1.467  X  16.3  =  244  ft.  (46) 

This  determines  one  point  (n')  on  the  distance  curve. 

In  order  to  determine  the  first  point  (b")  on  the  curved  portion 
of  the  acceleration  diagram,  an  increment  of  speed  must  be 
assumed. 

Let  dv  =  5  m.  p.  h.  or  v  +dv  =  25 . 4  m.  p.  h. 
The  gross  tractive  effort  on  the  characteristic  curve  corresponding 
to  25.4  m.  p.  h.  is 

T.E.  =400  lb. 
The  average  speed  for  this  increment  being  22.9  the  new  value 
of  train  resistance  (f)  will  be  found  from  the  resistance  curves 
to  be 

f'  =  i5  lb.  per  ton 
The  new  value  of  net  tractive  effort  is  therefore 

400 
p'  =  ^  ^    -15=49  lb.  per  ton.  (41) 

The  corresponding  value  of  acceleration  is 

49 
A'  =  — XI  .2:5=0.49  m.  p.  h.  p.  s.  (42) 

125  ^11  \T      / 

dt=        =10.2  sec.  (a-O 

•49 

The  coordinates  of  the  point  (b")  are  therefore: 

(V  +  dv)  =  25.4  m.  p.  h.  and  (t  +  dt)  =  26.5  sec. 

The  corresponding  point  on  the  distance  curve  is  found  as  follows 

20.4+25.4 
ds= -X  1.467  X  10.2  =  342  ft.  (46) 

5  =  244  +  342  =  586  ft.  from  start. 


74 


ELECTRIC    RAILWAY    ENGINEERING. 


Neg  acting  the  grade  which  is  encountered  at  a  distance  of  14 
ft.  beyond  the  above  point  and  continuing  the  above  "step  by 
step"  method  the  values  Hsted  in  Table  VII  may  be  determined 
and  the  acceleration  portion  of  the  diagram  plotted  to  the  point 
(i')  where  the  speed  becomes  constant. 

TABLE  VII. 
Calculated  Data,  Speed,  and  Distance  Time  Curves. 


dv 

V  +  dv 

dt 

t  +  dt 

ds 

s  +  ds 

S 

25-4 

10.2 

26.5 

342 

586 

3 

28.4 

10.7 

37-2 

421 

1007 

3 

314 

22  .2 

59-4 

974 

1981 

3 

34-4 

49.1 

108.5 

2370 

4351 

«  As  uming  the  total  braking  resistance  including  train  resistance 
b  =  150  lb.  per  ton  which,  of  course,  will  produce  a  deceleration  of 
1.5  m.  p.  h.  p.  s.,  a  straight  line  may  be  drawn  back  from 
T  =  159  sec.  with  the  above  deceleration  as  its  slope.  Such  a  line 
is  Tr',  Fig.  21. 

The  train  resistance  during  coasting  should  be  selected  as 
nearly  as  possible  to  the  value  which,  on  the  train  resistance 
curves  (Fig.  17),  corresponds  to  the  average  speed  expected  during 
the  coasting  period.  The  value  of  15  lb.  per  ton  is  often  taken 
arbitrarily  to  represent  this  resistance  and  will  therefo  e  be  used 
in  this  problem.  Since  this  corresponds  to  a  deceleration  of  o .  15 
m.  p.  h.  p.  s.,  a  line  with  th's  slope  is  drawn  in  the  position 
(f'k),  cutting  the  braking  line  at  point  k'. 

If  the  area  of  the  diagram  (Ob'b^f'k'T)  be  measured  with  the 
planimeter  it  will  be  found  to  contain  approximately  123  section 
squares.  With  the  particular  scales  of  speed  and  time  used  each 
square  is  equivalent  to  a  distance  of  36.6  ft.  The  diagram 
therefore  represents  a  distance  of  123  x  36.6  ft.  =4500  ft.  which 
is  greater  than  the  length  of  the  run.  The  coasting  line  must 
therefore  be  redrawn  parallel  with  itself  but  starting  with  a  lower 
initial  speed  until,  by  the  "cut  and  try"  method,  until  the  area 
of   the   diagram    is   found  to  correspond  to  the  length  of  the 


SPEED    DISTANCE,    CURRENT   AND    PO\\'ER    CURVES.  75 

run  in  feet.  Such  a  d'agram  is  that  bounded  by  the  lines 
(Ob'b"I'm'T),  Fig.  21.  If  the  true  coasting  resistance  be  now 
determined  it  will  be  found  to  be  13.5.  The  assumption  of  15 
was  therefore  conservative. 

The  distance  time  cur\'e  will  be  of  value  in  approximating  the 
correct  area  of  the  diagram.  The  values  of  distance  from  Table 
VII  plotted  against  time  would  produce  the  curve  of  distance 
covered  by  the  car  if  it  were  to  be  allowed  to  reach  constant  speed. 
How^ever,  since  the  power  is  shut  off  and  coasting  begun  at  a  speed 
of  27  .  5  m.  p.  h.,  a  new  distance  curve  must  be  determined  beyond 
this  point. 

The  distance  corresponding  to  point  (P)  is  found  as  follows: 

27.5  +  25.4 

Avg.  \  = =26.5  m.  p.  h. 

2 

t  =  33  sec. 

ds  =  26. 5  X  1.467  X  (33-26.  5)  =  252  ft.  (46) 

5=586+252  =  838  ft.  from  start. 

Continuing  the  calculations  of  distance  corresponding  to  the 
coasting  and  braking  portions  of  the  diagram  the  distance  time 
curve  (On'n"p')  is  determined  which  at  159  seconds  checks  very 
closely  the  length  of  the  run. 

Speed  and  Distance  Curves  for  Actual  Grades. — If  the 
actual  grades  listed  in  Table  \T  be  considered,  the  curves  take 
quite  a  different  and  more  complex  form.  Since  it  was  found  in 
the  previous  calculations  that  the  point  (b")  corresponded  to  a 
distance  but  14  ft.  short  of  (B),  Table  VI,  where  the  grade 
changes  to  6  per  cent,  it  will  introduce  little  error  and  simplify 
the  calculations  considerably  to  consider  the  grade  beginn'ng  at 
this  point. 

Since  the  6  per  cent,  grade  will  cause  an  immediate  reduction  in 
speed,  a  decrement  of  3  m.  p.  h.  will  be  assumed. 

dv  =  3  m.  p.  h.     V=22.4  m.  p.  h.     Avg.  V=23.9  m.  p.  h. 
(f")  at  23  . 9  m.  p.  h.  =  15  . 4  lb.  per  ton. 
T.E.  at  22.4  m.  p.  h.  =  600  lb. 

600 
p"=  -15.4-120= -39.4  lb.  (41) 

6.2s 


76  ELECTRIC    RAILWAY   ENGINEERING. 

Deceleration  =  0.394  m.  p.  h.  p.  s.  (42) 

dt  = =  7.6  sec. 

•394 

New  point  on  curve  has  coordinates  as  follows : 

V  =  22.4  m.  p.  h,  t  =  26. 5 +  7. 6  =  34. 1  sec. 

ds  =  23.9  X  1.467  X  7.6  =  266  ft.  (46) 

8  =  586+266  =  852  ft. 

The  corresponding  point  on  the  new  distance  time  curve  is  there- 
fore determined. 

Following  this  method,  being  careful  to  observe  every  change 
of  grade  at  its  correct  distance  from  the  start,  the  rather  irregular 
curve  (Ob'b"s''l"m''T)  results.  If  the  distance  corresponding  to 
each  of  the  steps  assumed  for  the  speed  time  curve  be  calculated 
the  distance  time  curve   (On'n"p")  may  be  plotted.     If  it  be 

ds 
remembered  that  the  slope  of  the  distance  time  curve        repre- 
sents speed,  the  effect  of  grades  in  reducing  speed  will  readily  be 
detected  if  the  two  distance  curves  are  compared. 

While  the  amounts  of  coasting  in  both  of  the  speed  time  curves 
considered  are  very  generous,  the  effects  of  grades  both  in  reducing 
the  possible  coasting  and  in  increasing  the  coasting  deceleration 
in  the  second  case  are  marked.  If  stops  were  necessary  in  this 
distance  the  coasting  periods  would  be  greatly  shortened  and 
possibly  eliminated  if  the  same  schedule  speed  were  maintained. 

Current  and  Power  Curves. ^ — The  gross  tractive  effort  during 
the  constant  acceleration  period  (Oa'),  Fig.  21,  was  found  to  be 
850  lb.  which  required  a  current  value  per  motor  of  84  amperes. 
During  the  first  half  of  this  same  period  plotted  to  the  same  scale 
on  Fig.  23  therefore,  the  current  per  pair  of  motors  in  a  four  motor 
equipment  is  84  amperes  while  the  current  per  car  is  168  amperes. 
In  the  second  or  parallel  half  of  the  period,  however,  the  corre- 
sponding values  of  current  are  168  and  336  amperes  respectively. 
In  determining  the  other  points  on  the  current  curve  such  as  the 
current  after  20  seconds  have  elapsed,  for  example,  it  is  found 
from  Fig.  21  that  the  speed  is  22 . 5  m.  p.  h.  Referring  to  the  speed 
characteristic.  Fig.  13,  the  corresponding  current  is  found  to  be  64 
amperes  per  motor  or  256  amperes  per  car  since  all  four  motors 


SPEED   DISTANCE,    CURRENT  AND   POWER   CURVES.  77 

are  now  operating  in  parallel.  This  value  is  plotted  against  a 
time  abscissa  of  20  sec.  on  Fig.  23.  Following  out  this 
method  the  current  required  for  operating  the  car  over  the  level 
track  will  be  represented  by  curve  (00"fkb"lq'),  Fig.  23,  while  the 
corresponding  current  with  the  actual  grades  introduced  is 
illustrated  in  curve  (00"fkb"mnq''). 

As  an  average  voltage  of  500  volts  has  been  assumed  on  this 
road  the  ordinates  of  the  two  similar  curves  of  Fig.  24  are  500 
times  those  of  Fig.  23  reduced  to  the  convenient  scale  of  kilowatts. 
If  these  curves  be  compared  with  the  speed  time  curve,  Fig.  21, 
the  ncreased  values  of  power  required  as  the  car  enters  the  grades 
will  be  noted. 

The  areas  of  the  two  kilowatt  time  diagrams,  Fig.  24,  are  3960 
and  12,100  kilowatt  seconds  respectively.  Applying  formula  (48) 
the  energy  required  by  the  level  run  is, 

3960 
E=  =1.1  kw.hr.  (48) 

3600 

while  that  of  a  run  invohdng  the  existing  grades  is, 

1 2 100 
E=     .      =3.36  kw.  hr.  (48) 

3000  » 

The  energy  consumptions  for  the  two  runs  expressed  in  watt 

hours  per  ton  mile  are, 

3960  X  1000  X  5280 
El-  =55.3  w.  hr. /ton  mile.  (49) 

3000  X  25  X  4200 

1 2 100  X  1000  X  5280 
E'l  =  -=  169  w.  hr. /ton  mile.  (49) 

3600  X  25  X  4200 

Since  the  rolling  stock  and  equipment  in  this  case  are  rather 
lighter  than  that  of  average  interurban  practice  the  value  of  55 . 3 
watt  hours  per  ton  mile  for  the  level  track  is  rather  a  low  figure 
while  the  steep  grades  in  the  latter  case  render  the  figure  169  for 
P^'i  rather  above  the  average.  The  very  fact,  however,  that  these 
values  of  energy  vary  over  so  wide  a  range  illustrates  the  marked 
effects  which  may  be  attributed  to  local  conditions  and  emphasizes 
the  necessity  of  a  complete  and  detailed  study  of  each  proposed 
road  before  accurate  estimates  can  be  made  of  its  cost  of  construc- 
tion or  dependable  conclusions  drawn  regarding  the  advisability 
of  its  installation. 


CHAPTER  X. 

Speed  Time  Curves  (Straight  Line). 

The  method  of  plotting  speed  time  curves  outlined  in  the 
previous  chapter  is  most  desirable  for  final  calculations  where 
considerable  accuracy  is  necessary.  For  preliminary  approxi- 
mate results,  however,  it  is  not  necessary  to  go  to  this  refinement 
and  the  so-called  "straight  line  "  speed  time  curve  described  below 
is  therefore  used. 


COMPARISON  OF  SPEED  -  TIME  CURVES 

30 

e 

b 

// 

/•isj 

X 

1 

^ 

H 

^ 

3=20 

Ah" 

^15 

a/ 

1 
1 

si 

S 

iv 

s 

•N 

H. 

1 

s 

\ 

^ 

N 

1 

1 
1 

^ 

N 

SI 

s 

10 

t 

\s 

N 

*^ 

^ 

0 

/ 

1 

1 

V 

\. 

V' 

5 

/ 

1 

t 

"•^1 

c" 

/ 

1 

!f 

U 

d 

30 


40 


60 


80  100 

Seconds 

Fig.    26. 


130        140 


160 


In  Fig.  26  will  be  found  reproduced  the  speed  time  curve 
(Oabcd)  calculated  in  Chapter  IX  for  a  straight  level  track,  Fig. 
21.  If,  now,  the  time  (Od)  and  the  distance,  represented  by  the 
area  (Oabcd),  are  kept  constant  and  the  acceleration  be  assumed 
constant,  i.e.,  the  acceleration  portion  of  the  figure  a  straight 
line,  the  diagram  (Oaec'd)  may  be  drawn  with  the  same  area  and 
with  the  average  assumed  coasting  and  braking  decelerations  of 
0.15  m.  p.  h.  p.  s.  and    1.5  m,  p.  h.  p.  s.  respectively.     Such 

78 


SPEED    TIME    CURVES. 


79 


a  chart,  although  it  may  vary  considerably  in  some  details  from 
the  more  accurately  drawn  curve  previously  considered,  is  exten- 
sively used  for  rapid  calculations  of  possible  schedules  for  a  given 
road  and  for  the  rough  determinations  of  recjuired  equipment  and 
preliminary  estimates. 

Granted  that  the  straight  line  diagram  is  sufficiently  accurate 
for  most  practical  purposes,  an  unlimited  number  of  similar  speed 
time  diagrams  may  be  plotted  for  the  same  distance  and  time  by 
varying  the  rate  of  acceleration  but  with  constant  coasting  and 
braking  decelerations.  Such  a  series  of  diagrams  for  a  i  mile 
run  in  120  sec.  appears  in  Fig.  27,^  in  which  (OBC)  represents 


\    1 

>v 

n 

,M^ 

r 

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yy 

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cN 

0  ;iO  40  60  80  100  ViO 

Seconds 

Fig.    27. — Typical  Speed  Time  Curves.     (V'arying  rates  of  Acceleration.) 


a  run  with  no  coasting  and  therefore  the  lowest  possible  rate  of 
acceleration,  while  the  other  extreme  case,  which  is  of  course 
theoretical  only,  is  represented  with  an  acceleration  (OA)  infi- 
nitely great.  Between  these  two  limiting  values  there  are  a  num- 
ber of  possible  selections  to  be  made,  the  gross  tractive  efforts 
listed  on  the  chart  including  the  net  effort  necessary  for  accelera- 
tion plus  the  15  lb.  per  ton  train  resistance  assumed  for  all 
diagrams.  It  should  be  noted  that  the  dotted  line  (AB)  is  the 
locus  of  maximum  speeds  for  all  diagrams. 

Furthermore,  if  the  distance  still  remain  constant  at  i  mile  and 
the  time  for  the  entire  run  be  varied  the  more  complete  chart, 
Fig.  28,^  results, which  is  made  up  of  a  series  of  charts  like  Fig.  27, 


'  Taken  from  "Electric  Traction,"  l)y  .\.  H.  Armstrong. 


8o 


ELECTRIC    RAILWAY   ENGINEERING. 


each  having  its  own  acceleration  variations  for  a  fixed  distance 
and  time.  The  dotted  curve  of  Fig.  28  represents  the  locus  of 
maximum  speeds  necessary  to  cover  the  distance  of  i  mile 
in  any  given  time  represented  as  an  abscissa.  For  example, 
if  it  be  desired  to  cover  the  mile  run  in  150  sec,  the  braking  line 
terminating  at  150  sec,  shows  the  maximum  speed  with  any 
acceleration  to  be  48  m.  p.  h.  corresponding  to  a  gross  tractive 
effort  of  51.2  lb.  per  ton.  If  other  rates  of  acceleration  are  pos- 
sible the  particular  chart  designated  by  the  point  51.2  may  be 
treated  as  outlined  in  Fig.  27. 


uu  - 

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Seconds 


180 


~'4U 


Fig.    28. — General  Speed  Time  Curves. 


These  charts  are  of  little  use,  however,  unless  readily  applicable 
to  various  lengths  of  run.  Such  application  may  be  made  in  the 
following  manner. 

It  can  be  readily  proved  geometrically  that  the  ratio  of  the  alti- 
tudes or  bases  of  two  similar  trapezoids  is  that  of  the  square  root 
of  their  areas.  The  speed-time  diagrams  which  have  been  con- 
sidered in  this  chapter  are  trapezoids  with  altitudes  representing 
maximum  speeds,  bases  representing  time,  and  therefore  with 
areas  expressed  in  terms  of  distance.  If  the  length  of  run  be 
changed,  keeping  the  same  acceleration  and  coasting  and  braking 


SPEED    TIME    CURVES.  8l 

decelerations,  the  diagrams  for  the  two  lengths  of  run  will  remain 
similar  and  the  following  formulae  may  be  derived  for  the  calcula- 
tion of  maximum  speed  and  time. 

T  =  Schedule  time  for  original  run. 
T'  =  Schedule  time  for  new  run. 
S  =  Distance  of  original  run. 
S'  =  Distance  of  new  run. 
Vj„  =  Maximum  speed  of  original  run. 
V'^  =  Maximum  speed  of  new  run. 

v.       IS'  .    , 

m  O 

As  an  illustration  of  the  use  of  these  formulae,  it  will  be  assumed 
that  the  speed-time  diagram  is  desired  for  a  run  one-half  the 
length  of  that  considered  in  the  previous  chapter  (2100  ft.), 
Fig.  26,  with  the  same  rate  of  acceleration,  coasting,  and  braking. 
From  the  diagram  the  following  values  may  be  scaled: 

T=(Od)  =  i59  sec. 
Vm=(ef)=28.5  m.  p.  h. 
S  =  42oo  ft. 

Substituting  in  equations  (50)  and  (51) 

T'  =  i59v/o-5  =  ii2.4sec.  (50) 

V'ni=  28.s\/o.s  =  20.1  m.  p.  h.  (51) 

Plotting  these  values,  the  diagram  (Oe'c"d')  results  and  there- 
fore represents  fairly  accurately  a  speed-time  curve  for  a  distance 
of  2100  ft.  with  a  minimum  of  labor  involved  in  its  determination. 

Energy  Calculations. — As  the  acceleration  was  assumed 
constant  in  the  above  diagrams,  it  is  usually  not  sufhciently 
accurate  to  derive  from  them  the  current  and  kilowatt-time  curves 
as  was  done  in  Chapters  VIIl  and  IX.  The  energy  required  for 
the  run  may  be  closely  approximated,  however,  by  the  following 
method,  which  may  also  be  used  to  advantage  as  a  check  on  the 
power-time  curves  when  the  latter  are  plotted  by  the  "step  by 
step"  method. 
6 


52  ELECTRIC    R.\ILWAY    ENGINEERING. 

Assume  the  following  nomenclature. 

V    =  Average  speed  in  m.  p.  h. 

Vj,   =  Initial  coasting  speed  in  m.  p.  h. 

Vj,  =  Initial  braking  speed  in  m.  p.  h. 

r  =  Total  train  resistance  in  lb.  per  ton  including  (f±g  +  c). 

El    =  Energy  in  watt  hours  per  ton  mile. 

2000W 

m    =  Mass  of  car  = . 

g 
b  =  Braking  force  at  periphery  of  car  wheel  in  lb.  per  ton. 

Sg    =  Distance  travelled  from  beginning  of  coasting  period  to 

stop  with  no  braking. 

S^  =  Distance  travelled  from  beginning  of  braking  period  to 

stop. 

tg   =Time  of  coasting  in  sec. 

tjj  =Time  of  braking  in  sec. 

V  X  5280  X  r  X  746 

Ei  =  — 7 77 —  =  1-99  r  (52) 

60  X  33000  V 

This  may  be  considered  with  little  error  to  be  (2  r). 

This  represents  in  simple  form  the  net  power  at  the  wheels  of 
the  car.  To  obtain  the  gross  input  to  motors  this  must  be  divided 
by  the  efficiency  of  the  motors  with  gears  included. 

Energy  During  the  Braking  Period. — Furthermore,  it  should 
be  noted  that  neither  equation  (52)  nor  the  formulas  of  Chapter 
VIII  include  the  power  required  to  stop  the  car.  To  determine 
this  power  exerted  during  the  braking  period,  proceed  as  follows: 

m(VbX  1.467)- 

-         -  (53) 

but 

e  =  Sb(b  +  r)  (54) 

therefore 

2000  W  (1.467  VJ^ 
WS,  (b  +  r)  = Vt         -  ^^^^ 

The  power  during  the  braking  period  is  therefore 

Ft.  lb.  per  min.     60  WS^  (b  +  r) 
H.  p.  = = 

33000  33000  tb 


SPEED   TIME   CURVES.  8^ 

or  simplified 

60  X2000W  (1.467  Vb)^  WV\ 

H.  p.=  =0. 121  (56) 

32.2  X  2  X  33000  tb  tb 

Coasting  Energy  and  Train  Resistance. — If,  however,  the 
above  reasoning  be  applied  to  the  results  of  a  coasting  test  in 
which  the  car  or  train  is  allowed  to  coast  to  a  standstill  from 
various  initial  speeds  the  train  resistance  may  be  calculated  thus 

2000  W  (1.467  VJ^ 
WS,r= ^^^^  (57) 

whence  V^^ 

r  =  66.8  -^  (58) 

By  thus  combining  the  straight  line  speed-time  charts  with  the 
calculation  of  energy  from  the  above  formulae,  a  rapid  although 
approximate  method  of  calculating  train  performance  is  provided 
which  will  be  found  of  great  convenience. 


PART  II. 

POWER  GENERATION  AND  DISTRIBUTION. 


CHAPTER  I. 

Substation  and  Power  Station  Load  Curves. 

Whereas  the  previous  chapters  have  been  devoted  to  the  oper- 
ation of  cars  and  trains  with  the  uhimate  object  of  determining 
the  demands  which  they  may  make  upon  the  power  distribution 
system,  it  is  now  necessary  to  study  the  combination  of  individual 
train  demands  and  their  connection  with  the  average  and  maxi- 
mum loads  on  the  substation  and  power  station. 

The  load  curves  of  substation  and  power  station  have  been 
treated  simultaneously  for  the  reason  that  the  substation  of  a 
large  urban  railroad  or  a  relatively  long  interurban  line  acts  as  a 
source  of  power  for  the  surrounding  distribution  system  and 
therefore,  as  far  as  the  determination  of  station  output  and 
capacity  are  concerned,  it  matters  little  whether  the  machines 
supplying  the  cars  are  in  turn  furnished  with  electrical  power 
over  a  high  tension  transmission  line  or  whether  they  are  driven 
by  engines  or  turbines. 

The  most  convenient  units  in  which  quickly  to  express  the 
power  demands  of  a  train  were  found  to  be  "watt  hours  per  ton 
mile."  This  demand  was  shown  to  vary  greatly  with  schedule 
speed,  weight  of  cars,  condition  and  profile  of  track,  length  of 
run,  etc.  It  is  clear,  therefore,  that  except  in  very  exceptional 
cases,  a  single  value  of  energy  cannot  be  applied  for  the  entire 
length  of  an  interurban  run  from  terminal  to  terminal.  Occa- 
sionally, however,  with  a  straight  level  right  of  way,  with  fairly 
constant  schedule  speed  throughout  the  run  and  with  all  cars  of 
about  the  same  size  and  weight,  an  average  value  of  energy  may 
be  used  for  all  cars  for  the  entire  run  and  the  average  substation 
demand  for  the  day  determined  as  follows: 

E  =  Energy  in  kilowatt  hours. 

El  =  Energy  of  car  in  watt  hours  per  ton  mile. 

W  =  Weight  of  car  in  tons. 

Sg  =  Length  of  section  supplied  by  station  in  miles. 

87 


88  ELECTRIC   RAILWAY   ENGINEERING. 

N  =  Number  of  trips  in  both  directions  over  section  per  day 

determined  from  graphical  train  schedule. 
Eff.  =  Efficiency  of  distribution  system  in  per  cent. 

The  energy  demand  upon  the  substation  in  a  day  is  therefore 

NWE1S3 
^  =  1000  xEfT.  (59) 

The  average  load  on  the  station  in  kilowatts  during  the  day  is 

E 

L  = . (60) 

Hours  operation  per  day 

If  it  were  not  for  the  excessive  current  taken  during  the  acceler- 
ation period  as  compared  with  the  full  speed  running  current, 
the  maximum  load  on  the  station  might  be  determined  by  multi- 
plying the  average  power  required  per  car  (average  ordinate  of 
the  kilowatt-time  diagram,  Fig,  24)  by  the  maximum  number  of 
cars  operating  upon  a  single  substation  section  at  any  one  time. 
This  method  will  usually  give  too  low  a  maximum  demand, 
however,  and  it  is  therefore  necessary  to  find  the  maximum 
number  of  cars  starting  simultaneously  on  a  single  section.  For 
such  cars  the  maximum,  ordinate  of  the  power  time  curve.  Fig.  24, 
must  be  used  together  with  the  average  ordinate  of  the  curves  of 
such  other  cars  as  may  be  running  upon  the  section  at  the  same 
time.  To  correctly  determine  the  number  of  cars  starting  at  any 
one  time  a  great  deal  of  judgment  and  knowledge  of  local  con- 
ditions is  necessary  in  addition  to  a  familiarity  with  the  train 
schedule.  If  there  be  a  siding  located  on  the  section  it  is  safe 
to  assume  at  least  two  cars  starting  simultaneously. 

While  this  method  of  determining  average  and  maximum  loads 
upon  a  substation  has  been  successfully  used  in  practice,  especially 
where  preliminary  estimates  only  were  involved  and  the  runs 
between  stations  on  a  given  section  were  quite  similar  in  all 
respects,  the  more  detailed  method  outlined  below  is  usually 
finally  adopted. 

A  series  of  speed,  current,  and  kilowatt-time  curves  are  plotted 
for  the  entire  road,  one  curve  for  each  run  between  stations.  If 
more  than  one  class  of  service,  such  as  local,  limited,  freight,  etc., 
is  proposed,  a  similar  series  of  curves  must  be  plotted  for  each. 


SUBSTATION  AND   POWER   STATION   LOAD   CURVES. 


89 


From  the  kilowatt-time  curves  it  is  possible  to  scale  off  the  area 
representing  the  energy  taken  by  the  car  or  train  during  any 
particular  interval  of  time  throughout  the  run.  The  combined 
areas  of  all  these  curves  may  readily  be  expressed  in  terms  of 
kilowatt  hours  per  run  or,  better,  the  portion  of  the  run  which  is 
shown  by  the  time  abscissa  and  train  schedule  to  be  on  a  given 
substation  section  may  be  thus  treated.  It  is  only  necessary,  there- 
fore, to  integrate  all  types  of  runs  throughout  the  day  on  a  given 
section  in  order  to  obtain  the  total  energy  and  average  load  on 
the  station  in  a  similar  manner  to  that  of  equations  (59)  and  (60). 


700 

r~ 

1 

SUBSTATION  LOAD  CURVE 

600 

nil 
■"Ml 

I 

, 

111 

1 

n 

.. 

III 
II  II 

1 
1 

1 

utii 

... 

_J 

I.. 

... 

... 

... 

... 

i\>  . 

!... 

._, 

500 

w 
^100 

0 
2  300 

200 

, 

■, 

11 

|- 

. 

100 

r- 

PI 

■1 

\ 

-I  ' 

1 

-1 

r-i 

r 

r~ 

["' 

r~ 

"ir 

~i 

■*  "1 

h 

6:00         8:60         10:00         12:00         2:00 
A.M.  P.M. 


4:00 
Fig.    29. 


6:00 


8:00 


10:00         12:00 
A.M. 


The  problem  may  be  carried  one  step  farther  if  necessary  and 
the  ordinates  of  kilowatt-time  diagrams  of  all  trains  on  the  section 
for  each  increment  of  time  added  together  to  form  the  most 
accurate  load  diagram  which  it  is  possible  to  predetermine  for 
the  substation. 

Many  modifications  of  these  two  methods  will  present  them- 
selves to  the  engineer  as  best  fitted  to  local  conditions  and  to  the 
degree  of  accuracy  required.  Fig,  29,  for  example,  is  a  load 
diagram  made  up  of  rectangular  areas,  each  representing  the 
average  kilowatt-hour  demand  of  all  cars  on  one  of  the  12 
mile  substation  sections  of  an  existing  interurban  road  at  a  given 
hour  of  the  day.  The  average  load  on  the  station  found  by 
taking  the  average  ordinate  of  this  curve  for  the  day  is  69.3  kw., 


go  ELECTRIC    R,A.ILWAY    ENGINEERING. 

while  the  maximum  demand  from  the  upper  curve  plotted  with 
reference  to  the  possible  number  of  cars  starting  simultaneously 
on  the  section  is  655  kw. 

In  plotting  station  load  curves  by  whatever  method,  it  must  be 
remembered  that  most  roads  have  not  only  the  daily  fluctuations 
of  load  which  will  be  shown  by  the  peaks  of  the  load  time  curve 
plotted  for  a  single  day,  but  there  is  usually  considerable  difference 
between  the  load  curves  for  the  various  seasons  of  year,  even  the 
train  schedule  being  changed  for  one  of  less  headway  in  the 
summer  season.  This  fact,  together  with  the  possibility  of 
sudden  daily  demands  due  to  special  attractions  along  the  line  of 
the  interurban  road,  especially  upon  holidays,  must  be  given 
careful  attention  in  applying  load  curves  to  the  location  and 
design  of  substations  and  power  stations. 

Load  Factor. — The  "load  factor"  of  a  station  for  a  given 
period  has  been  defined  as  the  ratio 

Average  power  demand 

. -, ,  (61) 

Maximum  power  demand 

although  it  is  often  considered  as  the  ratio  of  average  demand  to 
station  capacity.  The  load  factor,  as  determined  from  the  load 
curve  of  the  substation  in  this  particular  case  is  therefore, 

4^'- =10.6%  (61) 

While  a  low  load  factor  is  to  be  avoided  if  possible,  since  it 
follows  that  such  a  factor  involves  the  use  of  relatively  large 
station  equipment  operating  at  light  and  therefore  low  efficiency 
loads;  yet  in  interurban  practice  where  the  traffic  is  relatively 
light  and  the  trains  few  in  number  but  demanding  large  amounts 
of  power,  as  compared  with  the  city  systems,  it  is  hardly  possible 
to  improve  conditions  of  load  factor  to  any  great  extent  over  the 
particular  case  which  has  been  used  as  an  illustration. 


CHAPTER  -IL 

Distribution  System. 

The  circuit  which  the  propulsion  current  for  a  car  follows 
extends  from  the  feeder  panel  of  the  substation  over  the  out-going 
feeders  and  trolley  to  the  car  motors,  thence  through  the  rails 
back  to  the  substation  switchboard  or,  in  some  cases,  directly  to 
the  negative  terminal  of  the  converter.  The  voltage  at  the  sub- 
station is  maintained  constant,  usually  at  550  or  600  volts.  The 
current  flowing  over  the  above  circuit  causes  a  drop  of  potential 
in  proportion  to  the  resistance  of  the  entire  circuit  in  accordance 
with  Ohm's  law.  This  fall  of  potential  subtracted  from  the 
substation  potential  determines  the  voltage  at  the  car.  As  the 
latter  voltage  should  be  as  high  and  as  constant  as  possible  if 
good  service  is  to  be  maintained,  it  follows  that  the  resistance  of 
the  feeders  and  track  return  should  be  carefully  proportioned. 
The  latter  will  be  discussed  in  detail  under  the  subject  of  "  Bonds 
and  Bonding,"  Chapter  \T,  while  this  chapter  will  be  devoted  to 
the  study  of  the  overhead  trolley  and  feeder  system. 

On  interurban  roads  and  often  in  the  city  systems  the  trolley 
is  sectionalized  by  the  introduction  of  circuit  breakers  in  the 
trolley  wire  which  insulate  one  section  from  another.  Cables 
from  either  side  of  the  breaker  are  carried  to  a  pole  switch  by 
means  of  which  the  sections  may  be  connected  together  if  neces- 
sary. Each  section  is  generally  supplied  with  power  from  a 
single  substation  through  the  agency  of  feeders  paralleling  the 
trolley  for  a  portion  of  its  length.  The  trolley  wire  itself  for 
mechanical  reasons  is  usually  from  No.  00  to  Xo.  0000  B  &  S 
gauge  hard  drawn  copper  and  is  often  installed  double  with 
wires  about  6  in.  apart  but  electrically  connected  at  every 
hanger.  Where  the  current  required  is  considerable  this  prac- 
tice is  very  commendable,  for  the  second  trolley  replaces  an  equal 
amount  of  copper  which  would  otherwise  be  installed  in  the 
insulated  feeder  and,  what  is  of  greater  consequence,  it  eliminates 

91 


92  ELECTRIC   RAILWAY   ENGINEERING. 

all  overload  switches  and  frogs  in  the  trolley  wire  at  sidings,  the 
wires  being  spread  as  the  tracks  are  separated,  the  car  trolley 
always  remaining  on  the  right  wire.  With  the  size  of  trolley 
given,  together  with  a  well  ponded  track  of  known  weight  and 
resistance,  the  problem  resolves  itself  into  one  of  feeder  design. 

Since  the  problem  is  necessarily  treated  differently  for  inter- 
urban  and  urban  roads  the  former  will  be  first  considered.  The 
minimum  permissible  voltage  at  the  car  under  the  worst  condi- 
tions must  first  be  assumed.  While  this  voltage  drops  at  times 
in  interurban  practice  to  250  volts,  a  value  of  at  least  350  volts 

h 1 ^ 


r  "I  I     III  F'eeder  p  -i 

LI  I  II  I  V  I  I  I  I  II 


Trolley 

I       H h H 

H k H 

Fig.  30. — Continuous    Feeder  Distribution. 

should  be  used.  This  allows  250  volts  drop  in  the  distribution 
system  under  maximum  traffic  conditions.  Reference  to  the 
train  schedule  will  determine  this  maximum  condition  which 
usually  involves  two  cars  starting  simultaneously  and  possibly 
others  operating  on  the  same  section.  Assuming  the  simplest 
form  of  distribution,  Fig.  30,  with  the  feeder  paralleling  the  trol- 
ley for  the  entire  length  of  the  section  and  tapping  into  it  suf- 
ficiently often  so  that  they  may  be  considered  as  one  wire  of 
large  section,  the  following  solution  may  be  outlined. 

e  =  Permissible  voltage  drop. 
1  =  One-half  length  of  section  in  feet. 
1-j  =  Distance  of  car  (A)  in  feet. 
l2  =  Distance  of  two  cars  at  (B)  in  feet. 
I^=  Current  taken  by  one  car  at  (A). 
1b=  Current  taken  by  two  cars  at  (B). 
R^  =  Resistance  per  ft.  of  track  (two  rails). 
Ry^=  Combined  resistance  per  ft.  of  feeder  and  trolley, 
r  =  Resistance  of  copper  per  mil.  ft. 

As  in  mechanics  the  combined  loads  I^  and   1^,   determined 
from  the  current-time  curve,  may  be  considered  as  acting  through 


DISTRIBUTION    SYSTEM. 


93 


the  equivalent  distance  (Ig)  of  the  center  of  gravity  of  load  from 
the  substation  where 


Volts  drop  in  track  (e„)  =  lgRT(I^+  Ib) 
Allowable  drop  in  feeder  and  trolley 

e„  =  e-lgR,(I,+  l3) 

_e-I,R,(I,+  IJ 

Combined  area  of  feeder  and  trolley  in 

circular  mils  =  :^^ 


(62) 
(63) 
(64) 
(65) 

(66) 


Having  determined  the  necessary  combined  area  of  feeder  and 
trolley  from  equation  (66),  or  from  the  wire  tables,  the  known 
area  of  the  trolley  wire  or  wires  may  be  subtracted  and  the  neces- 
sary size  of  feeder  remains. 

Assuming  for  illustration  two  cars  whose  current-time  curves 
are  represented  in  Fig.  23  starting  3  miles  from  the  sub- 
station and  a  similar  car  running  at  full  speed  2  miles  from 
station.  The  trolley  consists  of  two  No.  4/0  B  &  S  wires  and 
the  track  is  of  70  lb.  rail  with  9  in.  bonds  equivalent  to 
one-half  the  rails  in  conductivity.  The  resistance  of  copper  may 
be  taken  as  10.6  ohms  per  mil.  ft. 

Armstrong  gives  the  resistance  of  third  rails  and  track  rails 
with  the  above  bonding  in  the  following  table. 

TABLE  VIII. 
Resistance  of  Thikd  Rail  and  Track. 


Wt.  of  rail  per  yd. 

1 

40 

50 

60 

70 

80 

90 

100 

no 

Third  rail  resistance,  ohms  per 

mile. 
Two  track  rails  resistance,  ohms 

per  mile. 

•093 
.066 

.074 
•053 

.062 
.044 

•053 
.038 

.046 
•033 

.042 
•033 

.038 
.027 

•034 
.024 

94  ELECTRIC    R-AILWAY    ENGINEERING. 

I^  from  Fig.  23  =  672  amp. 

Ig=  160  amp. 

^280(672  X  ^+160  X  2) 

L  =^ — — ~ -=14,800  ft.  =  2.8  mi.     (62) 

832 

Volts  drop  in  track  =8^,2  x  .038  x  2.8  =  88.5  "^'olts  (63) 

Allowable  drop  in  feeder  and  trolley  =  161. 5  volts  (64) 

161. 5 

R=.T=:; 'TT'  =.00001^1  or  .01  ;i  ohms  per  1000  ft. 

'"^     832  X  14800 

Corresponding  area  from  wire  table  =  800,000  cm. 
Two  4/0  trolley  wires  =  423,200  cm. 
Feeder  section  =  376,800  cm. 

Either  a  standard  350,000  or  400,000  cm.  cable  might  be  chosen. 
If,  in  place  of  isolated  sections  of  trolley,  the  wires  be  continu- 
ous from  terminal  to  terminal  and  the  substations  connected  in 


+2 
A 
X 


Fig.  31. — Division  of  Current  between  Substations. 

parallel  with  one  another  between  trolley  and  rail,  such  a  prob- 
lem as  that  assumed  above  would  involve  the  determination  of  the 
portion  of  the  current  per  car  which  was  supplied  from  each  of 
the  two  adjacent  stations.  Here  again  the  principles  of  mechanics 
may  be  applied  as  illustrated  in  Fig.  31  where  (A)  is  a  car  at 
distances  (IJ  and  (1 J  from  substations  No.  i  and  No.  2  respect- 
ively. If  the  car  is  drawing  a  current  (I  J  it  may  be  safely 
assumed  that  its  current  demand  on  substation  No.  i  is 

while  the  current  taken  from  No.  2  is 

I,=  Y  (68) 

With  this  understanding  a  problem  in  feeder  calculation 
similar  to  the  above  offers  no  additional  diiliculties. 

Each  half  of  the  section  in  Fig.  30  was  considered  independ- 
ently of  the  other  for  the  reason  that  the  feeders  and  trolleys  of 


DISTRIBUTION    SYSTEM.  95 

the  two  halves  of  the  section  are  in  parallel  and  therefore  the 
voltage  drop  in  one  does  not  affect  the  other.  The  solution  of 
a  problem  with  the  substation  located  at  the  end  of  the  section 
would  therefore  be  treated  in  a  similar  manner. 

In  many  cases,  however,  feeders  are  tapped  into  the  trolley  at 
infrequent  points,  thus  forming  a  network  whose  calculation  is 
slightly  more  involved.  Such  a  condition  is  illustrated  in  Fig.  32. 
The  feeder  is  tapped  to  the  trolley  at  the  two  points  (a)  and  (b) 
at  distances  from  the  station  of  (1)  and  (IJ  respectively.  Two 
cars  are  starting  at  (B)  at  a  distance  (1,)  from  the  station  with 
total  current  (I J. 

Volts  drop  in  track  =  l^R^^  n  (69) 

Allowable  drop  in  feeder  and  trolley  ep^  =  e— IgR^U  (70) 

U 1 ^ 


t 


s 


Trolley 


Fig.  32. — Feeders  with  Infrequent  Taps. 

In  any  branched  circuit  problem  such  as  this  it  is  always  most 
convenient  to  make  use  of  Kirchoff's  laws  which  may  be  stated 
as  follows: 

First,  "At  any  point  in  a  circuit,  the  sum  of  the  currents 
directed  toward  the  point  is  equal  to  the  sum  of  those  directed 
away  from  it." 

Second,  "In  any  closed  circuit  the  aJgebraic  sum  of  the  (IR) 
drops  is  equal  to  that  of  the  (e.  m.  f.  s.)." 

While  in  this  simple  problem  it  is  obvious  without  stating  such 
a  law  that  the  current  entering  the  cars  at  (B)  is  the  sum  of  the 
two  currents  arriving  at  (B)  by  the  two  paths  from  (a)  and  (b) 
respectively  and  also  that  the  drop  in  potential  between  (B)  and 
(b)  must  be  the  same  by  cither  path,  yet  in  complicated  networks, 
especially  in  city  streets,  the  statement  of  Kirchoff's  laws  in  this 
form  is  most  acceptable. 

The  resistance  from  (b)  to  (B)  direct  is  that  of  (l._.— li)  ft.  of 
trolley  or 

RbB=Rvva2-i.)  (71) 


96  ELECTRIC   RAILWAY   ENGINEERING. 

if  (R^)  represents  the  resistance  of  the  trolley  per  foot.  The 
corresponding  resistance  by  path  (a)  is 

RaB=Rwa-i2)+R.a-ii)  (72) 

with  (Rp)  representing  resistance  of  feeder  per  foot.  The  currents 
in  the  two  branches  may  now  be  calculated  from  the  two  equa- 
tions 

lB  =  Ia+Ib  (73) 

^a       ^bB  ,       . 

With  the  current  in  each  branch  known,  the  fall  of  potential 
between  point  (b)  and  the  car  (B)  may  be  determined  from  either 
of  the  equations 

eaB  =  Ia(RaB+Rba)  (75) 

eb3  =  IbRbB  (76) 

That  these  two  drops  in  voltage  are  identical  will  be  shown  more 
conclusively  by  substituting  in  (75)  the  value  of  current  (I J 
obtained  from  equation  (74). 

As  the  total  current  (IJ  is  flowing  through  the  feeder  between 
(b)  and  (S)  the  additional  drop  over  this  distance  is 

The  total  drop  in  the  overhead  conductors  between  substation 
and  car  is  therefore, 

ei  =  IbRbB+IbRpli  (77) 

If  the  feeder  had  been  tapped  into  the  trolley  at  the  substation 
(S)  in  addition  to  the  other  taps  a  second  network  would  have 
been  added  to  the  calculation,  but  the  method  of  solution  would 
not  have  been  changed.  In  fact,  any  network  may  be  readily 
solved  with  the  use  of  Kirchoff's  laws  if  taken  step  by  step. 

City  Systems. — The  principal  difference  between  the  calcula-  - 
tion  of  urban  and  interurban  feeder  systems  is  that  in  the  former 
it  is  necessary  to  consider  a  large  number  of  cars  per  section,  each 
drawing  an  average  current  which  may  be  readily  determined 
from  their  relative  current-time  curves  or  from  actual  tests  with 
meters  on  the  car  if  the  road  is  already  in  operation.  Such 
sections  may  ordinarily  be  considered  as  uniformly  loaded 
without  serious  error. 


DISTRIBUTION    SYSTEM  97 

Such  a  section,  represented  by  Fig.  ;^^,  may  be  treated  as  a 
uniformly  loaded  beam  in  mechanics  and  in  place  of  using  the 
individual  values  of  current  taken  by  each  car  at  a,  b,  c,  etc., 
the  total  current  of  all  cars  on  the  section  combined  may  be  con- 
sidered as  being  taken  from  the  mid-point,  distant  I/2  ft.  from 
the  station.  The  correctness  of  this  method  may  be  readily 
proved  by  integrating  the  voltage  drops  (ir  dl)  between  the 
limits  of  zero  and  the  length  of  the  line  (1)  where  (i)  represents 
the  current  per  foot  and  (r)  the  resistance  per  foot  respectively. 


-l- 


S 

i     I      1      1      !      ^     1     I     I     1     1     TT  Trolley 

a   b    <■    (' 

Fig.   TjT^. — Uniformally  Loaded  Distiibution  Section. 


Having  now  but  the  single  equivalent  current  to  consider,  the 
problem  may  be  solved  as  in  the  case  of  interurban  systems 
previously  described. 

Although  the  limiting  voltage  drop  is  always  the  first  con- 
sideration in  railway  feeders,  it  is  well  to  check  the  safe  carrying 
capacity  of  the  cable  selected  by  the  above  methods  with  the 
actual  current  which  is  flowing  therein,  the  safe  carrying  capac- 
ities for  open  wiring  being  readily  found  in  any  electrical  hand- 
book. 

Financial  Considerations. — While  the  foregoing  calculations 
will  give  the  proper  size  of  feeder  to  be  installed  for  a  given 
minimum  potential  at  the  car,  it  may  be  found  that  because  of 
too  great  an  assumed  distance  between  stations  or  for  other 
reasons  the  cost  of  the  copper  is  prohibitive.  Some  consideration 
must  therefore  be  given  to  the  amount  of  power  lost  in  the  distri- 
bution system,  and  the  relation  of  its  annual  cost  to  the  interest 
and  depreciation  on  the  copper  to  be  installed. 

If  the  I'-R  losses  be  summed  up  for  each  portion  of  the  distri- 
bution section  or  if  this  same  total  loss  be  obtained  from  the 
product  of  the  squared  current  by  the  equivalent  resistance  of 
the  overhead  conductors  and  rail  return,  the  efficiency  of  the 
7 


qS  electric  railway  engineering. 

distribution  system  and  the  annual  cost  of  power  lost  in  distri- 
bution may  be  determined  from  the  following  equations. 

Power  delivered  to  car 

Effy.  Dist.  System  =  - — , ; (78) 

Power  delivered  to  car+I^R  loss 


I  Cost  of  power 
Annual  cost       121?  jocc  ji^    cents    per 

of  distribu-=  (  x  hours  per  year)   x 

,  \    1000 

tion  loss 


kw.  hr.  at  d.  c.  (79) 
buses  of  sub- 
station. 


Kelvin's  law  states  that  the  most  economical  size  of  feeder 
to  install  is  that  in  which  the  annual  cost  of  power  loss  is  equal 
to  the  interest  and  depreciation  figured  on  first  cost  of  installa- 
tion. As  the  annual  cost  of  power  loss  for  a  given  length  of 
feeder  and  current  transmitted  will  decrease,  while  the  interest 
and  depreciation  charges  will  increase  as  the  size  of  the  cable 
increases,  curves  of  these  costs  plotted  with  size  of  cable  as 
abscissas  will  intersect  at  the  most  economical  size  of  wire  to  be 
installed.  Such  curves  plotted  for  a  current  of  100  amperes  in 
1000  ft.  of  feeder  with  interest  taken  at  6  per  cent,  and  depre- 
ciation at  2  per  cent,  will  be  found  from  Fig.  34  to  determine  a 
feeder  size  of  375,000  cm.  section  for  which  either  the  350,000 
or  400,000  cm.  standard  size  might  be  selected.  The  calcula- 
tions from  which  these  curves  were  plotted  involved  a  cost  of 
power  of  one  cent  per  kilowatt  hour  and  a  cost  of  copper 
installed  of  20  cents  per  pound. 

Since  any  one  of  these  feeder  calculations  taken  by  itself  may 
give  results  which  are  unfavorable  when  all  requirements  of  the 
distribution  system  are  considered,  it  is  the  duty  of  the  engineer 
to  calculate  the  proper  feeder  sizes  necessary  for  a  satisfactory 
line  drop,  to  check  these  calculations  for  carrying  capacity  and 
by  Kelvin's  law  and  then  to  determine  the  relative  weight  to  be 
given  to  the  considerations  of  fall  of  potential,  carrying  capacity, 
and  relative  cost  of  power  loss  in  the  particular  system  in  question. 

High  Voltage  Direct  Current  Distribution. — While  it  will 
be  seen  in  the  following  chapter  that  the  substation  connections 
are  somewhat  different  in  the  case  of  the  comparatively  few  roads 
operating  with  a  direct  current  voltage  of  1200  volts  on  the  trolley, 


DISTRIBUTION    SYSTEM. 


99 


the  distribution  system  is  materially  the  same  as  for  600  volts,  the 
potential  being  applied  between  trolley  and  rail  as  before  with 
the  necessary  feeders  paralleling  the  trolley  for  a  portion  of  the 
length  of  the  line  and  tapping  into  same  at  points  where  the 
voltage  would  otherwise  be  too  low. 

The  principal  difference  between  the  two  systems  is  the  greater 
distance  between  substations  and  therefore  the  fewer  substations 


-55 

c 
o 

|50 

3 

0) 

2.45 

o 
Q 

o)  3-5 

p 

a  30 


o  15 

o 


KELVIN'S  LAW 

1 

y 

\ 

■>< 

>f 

r 

\ 

t^ 

\ 

\ 

/ 

s 

^^ 

/ 

r 

/ 

v^ 

/ 

\ 

^^ 

.^ 

/ 

"^"^ 

—' 

3i 

OSS 

/ 

10 


;iOO,000       400,000       600,000       800,000      1,000,000 
Feeder  Size  in  Circular  Mils. 

Fig.    34. 

required.  As  the  distance  to  which  power  may  be  transmitted 
with  the  same  percentage  loss  and  first  cost  of  copper  varies 
directly  with  the  distance,  it  is  clear  that  with  1200  volt  supply 
the  substations  may  be  double  the  distance  apart;  and,  although 
the  distribution  feeders  may  be  longer,  they  have  to  transmit  but 
one-half  the  current  for  a  given  load,  and  are  therefore  but  one- 
half  the  area  necessary  for  600  volt  service.     The  method  of  cal- 


lOO 


ELECTRIC    RAILWAY    ENGINEERING. 


culation  of  feeder  sizes  is,  however,  identical  with  that  explained 
above. 

Single-phase  Distribution. — With  the  introduction  of  rail- 
way equipment  designed  for  operation  from  a  single-phase 
trolley,  the  distribution  system  is  changed  slightly.  While  the 
trolley  and  track  return  are  still  used,  the  voltages  applied  to  the 
trolley  have  been  increased  to  3300,  6600,  or  11,000  volts  and  in 


K--5-5— ->j 


r-F'-^fc^ 


Etiuiv.  to  No.  2  B.  i  S.  Copper 


Catenary  Cable  -6600  Volts 

M"-l  Slrand  Extra  Strenglh 

O.U.  Steel  Galv. 

Trolley  Wire, 
COUO  Volts 
1  -  No.  IIUOU 

B.  ^  b.  Grooved 
II.  D.  Copper 


Fig.  35. 


order  to  render  high  speed  current  collection  reliable  with  the 
further  advantage  of  longer  spans  and  better  insulation  the  so- 
called  "  catenary  "  construction  has  been  generally  adopted.  This 
design  involves  the  use  of  one  or  two  steel  messenger  wires  freely 
suspended  in  spans  of  several  hundred  feet  each,  with  a  convenient 
amount  of  sag,  which  in  turn  support  the  trolley  wire  by  means  of 
vertical  hangers  of  varying  length  spaced  about  ten  feet  apart  and 


DISTRIBUTION    SYSTEM. 


lOI 


SO  adjusted  that  the  trolley  wire  hangs  perfectly  level.  This 
eliminates  the  usual  vertical  rise  of  the  trolley  pole  at  supports 
with  the  accompanying  tendency  to  leave  the  wire  at  such  points 
when  operating  at  high  speed.  Such  single  catenary  construction 
on  the  Chicago,  Lake  Shore,  and  South  Bend  Railway  is  well  illus- 
trated by  the  typical  elevation,  Fig.  35,  while  the  more  complicated 
but  stronger  construction  used  by  the  X.  Y.  X.  H.  &  H.  R.  R. 
in  its  X^ew  York  terminal  electrification  will  be  found  in  Fig.  ^6. 


Fig. 


With  the  higher  trolley  voltages  used  with  this  system,  the 
substations,  if  necessary  at  all,  are  much  farther  apart  and 
trolley  sections  usually  longer.  Upon  the  shorter  roads  the 
transmission  line  and  substation  may  often  be  eliminated,  while 
the  possible  generation  of  power  at  6600  or  11,000  volts  often 
permits  the  step-up  and  step  down  transformers  to  be  omitted  as 
well  with  a  corresponding  decrease  in  first  cost  of  installation  and 
maintenance.  Three-phase  generation  is  generally  adopted 
because  of  the  lower  cost  and  small  size  of  three-phase  generators 
as  compared  with  single-phase  units.     This  necessitates  balancing 


I02 


ELECTRIC    RAILWAY    ENGINEERING. 


the  load  as  closely  as  possible  on  the  three  phases  which  is  best 
accomplished  by  entirely  insulating  adjacent  trolley  sections  from 
one  another  and  feeding  three  consecutive  sections  from  each  of 
the  three  phases.  Such  construction,  of  course,  will  not  permit 
tying  trolley  sections  together  in  case  of  emergency  as  in  direct 
current  distribution. 

In  some  instances  three-phase  generators  are  operated  as 
single-phase  machines  at  about  two-thirds  their  rating.  The 
simplicity   of   single-phase   distribution   and    the   ability   to    tie 


Fig. 


adjacent  sections  of  trolley  together  lend  some  advantages  to  this 
system  for  the  shorter  roads. 

The  calculation  of  single-phase  distribution  systems  is  based 
upon  the  same  laws  as  those  previously  outlined  in  detail,  it 
being  necessary  only  to  substitute  impedance  for  resistance  in 
determining  fall  of  potential  in  trolley  feeder  and  track.  It  will 
be  remembered  that  the  apparent  resistance  or  impedance  of  a 
conductor  to  the  flow  of  alternating  current  is  slightly  greater  than 
for  direct  current  depending  upon  the  size  and  material  of  the 
conductor  as  well  as  its  position  with  respect  to  the  return  circuit. 
Tables  of  impedances  for  different  sizes  and  spacings  of  wires 


DISTRIBUTION    SYSTEM.  IO3 

will  be  found  in  all  electrical  handbooks.  The  power  loss  calcu- 
lations for  a  given  current  are  identical  with  those  of  the  direct 
current  system  as  the  impedance  does  not  enter  these  equations. 

Third  Rail  Distribution. — Practical  difficulties  in  collecting 
large  currents  at  high  speeds  by  means  of  an  overhead  trolley  have 
led  to  the  installation  of  an  insulated  third  rail  or  contact  rail  at 
the  side  and  slightly  above  the  running  rails  to  which  the  positive 
feeders  are  connected  and  from  which  the  current  is  collected  by 
one  or  more  iron  contact  shoes  carried  by  each  car.  These  shoes 
ordinarily  bear  on  the  head  of  the  rail  with  their  own  weight  but 
in  some  instances  the  third  rail  is  inverted  and  protected  with  an 
insulating  shield,  in  which  case  the  shoe  is  pressed  upward  against 
the  head  of  the  rail  by  means  of  springs.  Typical  protected  third 
rail  construction  is  illustrated  in  Fig.  37,  which  shows  very 
clearly  the  necessary  break  in  the  third  rail  at  street  crossings. 
This  break  is  electrically  bridged  by  means  of  a  copper  cable 
installed  in  conduit  under  the  crossing. 

The  calculations  for  third  rail  installations  are  identical  with 
those  for  direct  current  trolley  distribution,  the  resistances  of  the 
third  rail,  Table  VIII,  replacing  those  of  the  trolley  wires. 

The  relative  advantages  and  disadvantages  of  the  various 
systems  whose  method  of  distribution  has  been  briefly  described 
above  will  be  compared  in  Part  IV,  Chapter  I. 


CHAPTER  III. 
Substation  Location  and  Design. 

There  is  probably  no  question  which  the  engineer  of  a  pro- 
posed electric  railway  system  has  to  decide  that  is  more  depend- 
ent upon  good  engineering  judgment  and  common  sense  than 
that  of  the  location  of  substations  and  power  stations.  Many 
theoretical  rules  and  formulcC  have  been  devised  for  the  purpose 
of  calculating  the  most  economical  location  of  such  a  station  and 
many  of  these  must  be  given  consideration  and  granted  their 
proper  weight  in  the  final  decision,  but  they  are  of  little  value 
when  taken  alone  and  often  lead  to  serious  errors  when  given  too 
much  prominence  or  when  adopted  with  too  little  reference  to 
local  engineering  and  financial  relations. 

With  this  foreword  a  few  of  the  most  important  of  these  theories 
will  be  discussed,  their  relative  importance  being  decided  in 
each  case  by  local  and  particularly  by  financial  conditions.  If 
the  distinction  between  the  design  of  alternating  current  sub- 
stations for  single-phase  lines  and  substations  supplying  600 
volt  direct  current  as  subsequently  outlined  are  kept  in  mind 
the  following  considerations  may  readily  be  applied  to  either  typp 
of  station. 

Substation  Location. — When  a  substation  is  being  con- 
sidered whose  function  it  is  to  supply  power  to  a  network  of  lines 
in  a  limited  district  of  a  large  city  system,  one  of  the  important 
considerations,  as  in  the  case  of  the  power  station,  is  to  locate 
the  station  as  nearly  as  possible  at  the  center  of  gravity  of  the 
load.  This  center  of  gravity  may  be  conveniently  determined 
graphically  as  in  problems  in  mechanics  as  follows.  Locate  the 
principal  centers  of  distribution  in  the  district,  such  as  promi- 
nent street  crossings  and  points  from  which  several  feeders 
radiate  and  determine  the  average  load  at  these  points  as  well 
as  their  distance  apart.  These  may  be  graphically  represented 
as  in  Fig.  38  with  the  loa^is  considered  as  weights  at  the  corners 

104 


SUBSTATION    LOCATION   AND    DESIGN. 


105 


of  the  diagram  which  is  drawn  to  a  convenient  scale  of  distance. 
The  center  of  gravity  of  the  loads  (A)  and  (B)  would  obviously 


be  at  (E)  where 


AE 


500 


and  AB  or  (AE+BE)  =  i 


5  mi.  while 


(D)  and  (C)  might  be  combined  into  a  single  load  of  1650  kw. 
at  (F)  where 

DF     1000 

CF^  650 
The  center  of  gravity  of  (E)  and  (F)  with  loads  of  700  and  1650 
respectively  located  at  (G)  will  therefore  be  the  center  of  gravity 
of  the  system  and  from  the  standpoint  alone  of  supplying  the 
loads  most  economicallv  this  should  be  the  location  of  the  station. 


B-aCO  K.W. 


D-650K.W. 

Fig.  38. — Center  of  gravity  of  power  demands. 

With  the  more  common  problem,  however,  of  locating  substa 
tions  for  interurban  lines  where  the  loads  are  usually  located  in  a 
single  straight  line,  the  question  to  be  decided  is  how  far  apart 
should  the  stations  be  placed  in  the  single  direction  and  there- 
fore how  many  and  what  capacity  stations  are  necessary.  The 
maximum  distance  between  stations  is  limited  by  the  voltage  of 
the  distribution  system  and  in  the  case  of  the  more  common  600 
volt  direct  current  distribution  the  distance  between  stations 
seldom  exceeds  12  miles,  each  station  feeding  6  miles  in  either 
direction.  Whether  this  distance  shall  be  diminished  or  slightly 
increased  in  each  particular  case  depends  largely  upon  the 
following  considerations. 


Io6  ELECTRIC    RAILWAY    ENGINEERING. 

As  the  number  of  substations  for  a  given  road  is  increased 
and  therefore  the  distance  between  them  diminished  the  govern- 
ing factors  will  vary  as  outlined  below. 

The  total  cost  of  buildings  and  real  estate  will  usually  in- 
crease in  direct  proportion  to  the  increase  in  the  number  of  sta- 
tions. This  statement  is,  of  course,  subject  to  the  qualification 
that  such  spacing  of  stations  does  not  locate  one  or  more  of  them 
in  the  centers  of  towns  or  cities,  or  in  such  other  places  as  may 
increase  their  cost  from  the  standpoint  of  high  land  values  or 
expensive  architectural  effects. 

The  cost  of  attendance  will  increase  directly  with  the  number 
of  stations  as  the  increased  capacity  of  the  fewer  stations  would 
seldom  if  ever  require  more  attendants  than  the  small  station 
unless  the  station  were  located  in  a  congested  city  district  where 
the  high  cost  of  real  estate  necessitated  double  decking  the  station. 

The  substation  equipment  will  cost  more  with  the  increased 
number  of  stations  but  not  proportionately  more.  Whereas 
much  of  the  equipment  will  have  to  be  duplicated  with  each 
station  that  is  added  and  although  the  cost  of  small  units  is 
greater  per  kilowatt  capacity  than  that  of  large  machines,  yet  if  all 
the  stations  considered  are  of  fairly  large  capacity  the  relay  capacity 
necessary  for  overloads  of  long  duration  and  for  emergency  use 
will  not  be  as  great  with  an  increased  number  of  stations.  This 
may  be  illustrated  by  assuming  a  total  average  demand  upon  all 
substations  of  2000  kw.  If  two  substations  are  decided  upon, 
it  would  be  good  practice  to  install  three  500  kw.  units  in  each, 
or  a  total  of  3000  kw.,  thus  leaving  one  500  kw.  machine  in  each 
station  as  a  relay.  If,  however,  four  stations  seem  advisable  of 
500  kw.  average  demand  each,  it  is  probable  that  three  250 
kw.  units  would  be  used  in  each  station  requiring  the  same  total 
of  3000  kw.  While  the  switchboards,  wiring,  lightning  pro- 
tection, etc.,  would  therefore  cost  double  the  amount  for  the 
four  stations,  the  machines  and  transformers  would  be  increased 
in  cost  only  by  the  increase  per  kilowatt  of  small  as  compared 
with  large  units,  which  increase  between  units  of  250  and  500 
kw.  is  not  great.  Where  the  total  demand  on  all  stations  is  much 
less  than  that  assumed  in  this  case,  however,  the  small  station 
is  at  a  disadvantage  with  respect  to  relay  capacity  and  the  in- 


SUBSTATION    LOCATION   AND    DESIGN.  IO7 

creased  cost  of  eciuipment  may  equal  if  not  exceed  the  rate  of 
increase  in  number  of  stations. 

The  losses  in  substation  machinery  will  increase  slightly 
with  increase  in  the  number  of  stations  because  of  the  lower 
efficiency  of  smaller  units  and  the  increased  no-load  losses  of  the 
larger  number  of  machines  running  light  or  idle  for  a  portion  of 
the  time  as  is  often  the  case  in  interurban  stations. 

The  cost  of  distribution  copper  and  the  losses  in  the  distri- 
bution system  will  decrease  with  the  increase  in  the  number  of 
stations,  as  the  length  and  .therefore  the  cost  and  resistance  of 
feeders  will  decrease  as  the  stations  are  moved  nearer  together. 

In  order  to  reduce  all  of  these  quantities  to  common  terms 
for  comparison,  an  annual  charge  representing  a  certain  per- 
determined  percentage  of  the  first  costs  involved  must  be  com- 
bined with  the  annual  cost  of  attendance,  maintenance,  and  power 
losses.  This  percentage  of  the  first  cost  which  becomes  an 
annual  charge  in  all  estimates  of  this  nature  is  termed  a  "fixed 
charge"  and  involves  interest  on  investment,  taxes  if  any,  insur- 
ance and  depreciation  on  the  equipment.  This  charge  may  be 
accurately  estimated  in  each  instance  but  is  often  assumed  a  total 
of  1 1  per  cent,  of  the  first  cost  whenever  local  conditions  are  such 
as  not  to  eliminate  any  of  the  above  mentioned  items  involved 
in  its  makeup.  If,  therefore,  a  curve  be  plotted  between  ordinates 
representing  the  sum  of  fixed  charges,  annual  cost  of  power  losses, 
and  maintenance  and  abscissae  expressed  in  terms  of  number  of 
substations,  the  total  annual  cost  curve  will  result  and  because  of 
the  fact  that  some  of  the  factors  are  increasing  and  some  decreas- 
ing with  an  increase  in  the  number  of  stations,  a  minimum 
point  on  the  curve  will  be  found  which  will  denote  the  proper 
number  of  substations  to  install  and  therefore  the  distance 
between  stations,  considered  solely  from  the  standpoint  of  the 
factors  involved  in  the  curve. 

Such  a  method  as  that  outlined  above  appears  rather  involved, 
requiring  as  it  does  at  least  a  tentative  station  location,  design  of 
equipment,  and  feeder  loss  calculation  for  each  group  of  stations 
considered.  Since  the  capacity  alone  and  not  the  detailed  plan  of 
the  station  changes  with  increased  number  of  stations,  and  as  the 
feeder  losses  in  an   interurban   system  will  vary  approximately 


Io8  ELECTRIC    ILAILWAY    ENGINEERING. 

in  proportion  to  the  length  of  the  feeders,  the  number  of  calcula- 
tions necessary  for  such  a  curve  is  not  great  and,  as  the  cost  varia- 
tions when  thus  graphically  plotted  are  easily  studied  and  com- 
pared, the  solution  is  well  worthy  of  serious  consideration. 
Chapter  II  on  the  "Distribution  System"  will  aid  materially  in 
the  construction  of  these  curves. 

It  will  be  noted  that  nothing  was  said  regarding  the  variation 
of  transmission  line  costs  and  losses  in  the  above  discussion. 
While  these  factors  may  occasionally  enter  the  problem  in  the 
case  of  city  stations  with  underground  high  tension  lines,  yet  in 
the  case  of  interurban  installations  the  transmission  line  usually 
parallels  the  road  for  nearly  the  entire  distance,  often  looping 
through  each  of  the  substations  en  route.  With  such  construction, 
h  will  be  seen,  the  transmission  line  first  cost  and  annual  losses 
will  not  vary  appreciably  with  substation  location,  especially  for 
the  reason  that  in  the  case  of  long  lines  with  relatively  small 
power  requirements  the  transmission  line  wire  is  much  larger 
than  that  required  for  any  electrical  considerations  because  of  the 
mechanical  strength  needed.  Even  in  high  tension  underground 
systems  the  substations  are  usually  tied  together  by  such  a  net- 
work of  primary  feeders  for  the  sake  of  reliability  of  service 
that  the  first  cost  and  annual  losses  in  the  primary  system  may 
be  considered  practically  independent  of  the  number  of  stations 
providing  the  total  output  does  not  change. 

Another  important  factor  which  should  not  be  overlooked, 
especially  when  express  and  freight  service  is  contemplated,  is 
the  question  of  com.bining  the  substation,  waiting  station,  and 
freight  or  express  depot  into  one  building  with  a  material  saving 
in  the  item  of  substation  attendance,  since  the  substation  operator 
can  often  attend  to  the  other  duties  of  the  passenger  station  as  well. 

If  the  station  be  not  operated  throughout  the  twenty-four  hours 
the  question  of  living  accommodations  for  station  attendants  must 
be  given  some  attention  as  the  theoretical  determination  might 
locate  the  substations  in  localities  where  no  attendants  would  be 
willing  to  live  even  though  the  railway  company  provided  living 
apartments  in  the  substation  building  as  is  often  the  case.  W^ith 
some  of  the  shorter  systems  it  is  possible  to  connect  the  various 
sections  of  trolley  and  feeders  through  the  substation  switchboard 


SUBSTATION    LOCATION   AND    DESIGN.  lOQ 

to  the  600  volt  direct  current  supply  of  the  power  station  and 
thereby  enable  the  first  car  in  the  morning  to  run  over  the  Hne 
before  the  substations  are  started.  With  such  an  arrangement 
the  operators  may  live  in  the  nearest  town  to  the  substation. 

Substation  Design. — Assuming  the  most  common  type  of  sub- 
station whose  function  it  is  to  transform  energy  supplied  by  a  high 
tension  alternating  current  transmission  line  into  direct  current 
at  approximately  600  volts,  the  principal  factors  entering  into  its 
design  will  be  briefly  discussed. 

With  a  knowledge  of  the  load  demand  curve  and  the  efficiency 
of  the  distribution  system  and  with  the  number  and  location  of 
substations  determined,  the  average  and  maximum  loads  on  the 
substation  may  be  found  as  outlined  in  Chapter  I.  To  decide 
upon  the  proper  capacity  of  units  to  be  installed,  however,  is 
largely  a  matter  of  good  judgment.  Since  it  is  now  standard 
practice  to  rate  electrical  machinery  for  a  possible  25  per  cent, 
overload  for  two  hours  without  overheating,  the  duration  of  the 
peak  load  must  be  studied  as  well  as  its  magnitude.  It  must  also 
be  known  whether  or  not  there  is  a  possibility  of  greater  loads  at 
any  time  during  the  year  and  also  what  the  growth  in  power 
demand  is  likely  to  be  within  the  next  few  years.  With  these 
facts  in  mind  it  is  well  to  provide  for  the  average  power  by  the 
installation  of  two  or  more  units,  usually  leaving  one  unit  as  a 
relay  in  case  of  emergency.  This  relay  unit  should  ordinarily  be 
as  large  as  the  other  units  in  the  station  in  order  that  it  may  take 
the  place  of  another  machine  in  case  of  break  down.  Units  of 
less  than  200  kw.  are  seldom  installed  and  if  the  average  load 
is  less  than  this  value,  the  200  kw.  machines  are  usually  run 
at  light  load  rather  than  install  smaller  units.  This  procedure 
involves  relatively  large  idle  relay  capacity  as  well  but  the  smallest 
units  are  usually  less  reliable  and  offer  little  reserve  capacity  or 
inertia  in  case  of  sudden  overloads. 

In  the  problem  taken  for  illustration  in  Chapter  I  the  average 
demand  is  69.3  kw.,  while  the  maximum  demand  is  655  kw. 
The  low  average  value  is  due  to  the  fact  that  during  several  rather 
long  periods  there  is  no  car  on  the  section  and  the  unit  is  there- 
fore running  light.  Further  study  of  the  curve  will  show  that  a 
load  of  130  kw.  is  maintained  for  an  hour  at  a  time  while  peaks 


no  ELECTRIC    RAILWAY    ENGINEERING. 

of  260  k\v.  exist  for  fifteen  minutes.  A  200  k\v.  machine  would 
supply  the  average  load  and  these  latter  peak  loads  but  would  not 
be  of  sufficient  capacity  for  the  peaks  of  655  kw.  caused  by  the 
simultaneous  starting  of  two  cars.  A  300  kw.  unit  would  there- 
fore be  necessary  for  this  station  as  it  could  withstand  the  momen- 
tary overload  of  100  per  cent.  This  case  is  a  good  example  of  the 
necessity  of  taking  the  overloads  and  their  duration  into  account 
in  such  determinations. 

Synchronous  Converter  vs.  Motor  Generator. — Having 
determined  upon  the  proper  capacity  for  the  unit  a  decision 
should  be  made  between  the  synchronous  converter  and  the  motor 
generator.  The  former  machine  consists  of  a  synchronous  alter- 
nating current  motor  and  direct  current  generator  combined  into 
a  single  unit  with  but  one  frame,  armature,  and  field.  It  is  really 
a  direct  current  generator  with  the  armature  winding  tapped  to 
slip  rings  at  symmetrical  points,  which  rings  are  supplied  with 
alternating  current  as  in  the  case  of  the  synchronous  motor.  The 
motor  generator,  as  its  name  implies,  is  an  alternating  current 
motor  direct  connected  to  a  direct  current  generator.  The  motor 
may  be  either  of  the  synchronous  or  induction  type. 

The  advantages  of  each  type  of  unit  for  railway  substation 
service  are  briefly  set  forth  in  the  following  paragraphs: 

Advantages  of  Motor  Generator. — The  ratio  between  a.  c. 
and  d.  c.  voltage  is  not  fixed.  For  transmission  voltages  not 
exceeding  13,000  this  set  m.ay  therefore  be  operated  without  step- 
down  transformers  if  the  motor  be  wound  for  transmission  line 
voltage. 

The  d.  c.  voltage  may  be  readily  controlled  by  means  of  the 
generator  field  rheostat  without  affecting  the  a.  c.  voltage  or  power 
factor. 

The  d.  c.  generator  may  be  automatically  compounded  or 
ovei -compounded  without  auxiliary  apparatus.  The  converter 
requires  an  external  reactance  in  addition  to  the  series  field. 

The  motor  generator  is  not  as  sensitive  to  commutation 
troubles,  especially  upon  sudden  overloads,  as  the  converter. 

"Hunting,"  or  the  periodic  variation  in  speed  on  either  side 
of  an  average  value,  with  the  usual  accompaniments  of  poor 
commutation  and   "arcing  over"   are  less   marked  in  the  syn- 


SUBSTATION    LOCATION   AND    DESIGN.  Ill 

chronous  motor  generator  set  because  of  its  greater  inertia,  while 
they  are  entirely  absent  in  the  induction  motor  set. 

The  power  factor  of  the  synchronous  motor  generator  set 
is  controlled  quite  as  easily  as  with  the  converter.  The  induction 
motor  set,  of  course,  has  the  disadvantage  of  low  uncontrollable 
power  factor. 

Advantages  of  Synchronous  Converter. — This  machine  has 
a  higher  efficiency. 

Its  rating  for  a  given  size  of  frame  is  much  higher. 

The  floor  area  taken  up  is  considerably  less. 

Its  cost  is  less  for  a  given  capacity  although,  in  cases  where 
the  adoption  of  the  motor  generator  enables  the  transformers  to 
be  eliminated,  the  first  cost  of  the  converter  with  transformers  is 
about  the  same  as  that  of  the  motor  generator  alone. 

Methods  of  Starting. — Upon  comparison  of  methods  of  start- 
ing there  is  found  to  be  no  choice  between  the  two  types  of 
machines  since  both  may  be  started  from  either  the  d.  c.  or  a.  c. 
side  and  with  the  latter  method  both  machines  may  be  started 
by  either  the  variable  voltage  method  of  the  General  Electric 
Company  or  the  auxiliary  induction  motor  method  of  the  West- 
inghouse  Company.  If  the  direct  current  method  of  starting  is 
adopted  a  starting  rheostat  must  be  provided  which  in  turn  will 
be  controlled  by  a  multi-point  switch  usually  mounted  on  the 
switchboard.  This  switch  starts  the  converter  from  the  600  volt 
feeder  system  as  an  ordinary  d.  c.  motor,  gradually  cutting  out 
resistance  until  the  motor  comes  up  to  speed,  when  the  rna^ 
d.  c.  switch  may  be  closed.  The  speed  may  then  be  varied  by 
changing  the  field  excitation  until  the  a.  c.  side  is  synchronized, 
by  means  of  the 'synchroscope  or  synchronizing  lamps,  as  in 
the  case  of  the  synchronous  motor  or  alternator. 

With  the  variable  voltage  method  of  starting  low  voltage  taps 
are  taken  from  the  bank  of  transformers  to  a  double  throw 
switch  usually  located  on  a  separate  panel  near  the  converter. 
When  the  switch  is  thrown  down  a  low  voltage,  usually  a})out 
one-third  rated  voltage,  is  impressed  on  the  armature  of  the 
converter  and  the  machine  starts  as  an  induction  motor.  As  the 
converter  approaches  full  speed  the  armature  is  supplied  with 
full  voltage  by  throwing  the  starting  switch  into  the  "up"  position. 


112  ELECTRIC    RAILWAY    ENGINEERING. 

This  method  requires  a  rather  large  starting  current  at  low  power 
factor  but  has  the  advantage  of  eliminating  the  necessity  of  syn- 
chronizing. In  both  the  above  methods  it  is  necessary  to  open 
the  shunt  field  winding  of  the  converter  in  several  places  in  order 
that  the  excessive  voltage  otherwise  induced  in  the  many  turns 
of  the  field  by  the  large  circulating  currents  in  the  armature  may 
not  puncture  the  field  winding. 

If  the  auxiliary  induction  motor  method  be  used  a  small 
induction  motor,  sufficiently  large  to  start  the  converter  with 
no  load  and  bring  it  to  slightly  above  synchronous  speed,  is 
mounted  on  the  end  of  the  converter  shaft.  This  motor  is  usually 
operated  by  means  of  a  three  pole  starting  switch  on  the  switch- 
board which  is  supplied  with  power  from  auxiliary  transformer 
connections.  As  the  converter  reaches  its  proper  speed  it  is 
synchronized  with  the  transmission  line  as  in  the  first  case.  The 
starting  motor  is  then  cut  out  of  circuit. 

As  each  type  of  unit  has  many  advantages  and  as  both  are  in 
general  use  in  railway  substations  it  will  be  left  to  the  engineer 
of  each  particular  system  to  weigh  the  advantages  and  dis- 
advantages with  reference  to  the  local  conditions  under  which 
they  are  to  operate  and  to  make  the  decision.  It  may  be  safely 
stated  that  the  converter  was  at  first  installed  almost  universally 
in  railway  substations,  but  during  the  last  few  years  the  motor 
generator  set  has  proved  a  formidable  competitor  and  has  been 
installed  in  many  instances  largely  because  of  the  commutation 
and  hunting  troubles  which  have  been  connected  with  the  opera- 
tion of  the  converter  in  practice. 

Transformers. — If  synchronous  converters  are  installed  to 
maintain  a  constant  direct  current  potential,  the  secondary  alter- 
nating current  voltage  which  must  be  supplied  to  them  is  at  once 
determined,  since  with  the  single  armature  of  the  converter  there 
is  a  definite  ratio  between  a.  c.  and  d.  c.  voltages.  This  usually 
rec|uires  the  installation  of  step-down  transformers  in  order  to 
lower  the  transmission  line  voltage  to  that  value  required  by  the 
converters.  Even  if  motor  generators  are  installed  the  trans- 
mission line  voltage  for  interurban  roads  is  usually  so  high  that 
transformers  are  necessary  in  the  substation. 

In  Fig.  39  will   be  found  an    efificiency  curve   for  a  750  kw. 


SUBSTATION    LOCATION   AND    DESIGN.  II3 

three-phase  synchronous  converter  from  which  it  will  be  noted 
that  ahhough  the  efficiency  falls  off  with  light  loads  as  with  all 
other  electrical  machines,  it  may  be  considered  constant  for  all 
loads  above  50  per  cent  of  its  rating.  The  rated  capacity  of 
the  converter  divided  by  this  efficiency  constant  will  give  the 
necessary  transformer  output.  In  this  country  almost  universal 
preference  has  been  shown  for  single-phase  transformers  com- 
bined into  banks,  usually  of  three  each,  in  place  of  three-phase 


100 

3"  90 


5  70 


~ 

1 

1    1 

EFFICIENCY  OF  A  750  K.W.   ROTARY  CONVERTER 



/ 

V^ 

^ 

/ 

/ 

/ 

/ 

1 

30 


dO 


60  80         100 

Percent  Load 

Fig.  39. 


120       MO 


160 


transformers.  This  is  largely  because  of  the  increased  flexibility 
of  the  system  with  smaller  units  and  the  avoidance  of  crippling 
the  transformers  of  all  phases  in  case  of  damage  to  a  single  unit. 
The  rating  of  each  transformer  will  therefore  be  determined  as 
follows  in  the  more  common  three-phase  installation. 

Converter  kw. 

Transformer  kw.  = .,. —  (80) 

3  X  converter  effy. 

A  bank  of  three  transformers,  each  of  the  above  rating,  should  be 
installed  for  each  converter  or  motor  generator  usually  with 
switches  in  both  high  and  low  tension  connections.  The  trans- 
former connections  may  be  either  the  well  known  "delta"  or 
"star"  on  both  primary  and  secondary,  or  either  set  of  windings 
may  be  connected  "delta"  with  the  other  "star"  remembering 
8 


114  ELECTRIC    R.\ILWAY    ENGINEERING. 

that  with  fixed  transmission  line  and  converter  voltages  the 
rated  voltage  of  the  transformers  will  be  less  than  line  voltage 

in  the  ratio  of       ,     if  the  "star"  connection  be  adopted.     The 

"delta"  connection  has  the  advantage  of  continuing  three-phase 
operation  with  two  transformers  "V"  connected  in  case  of  damage 
to  one  unit  without  change  of  connections.  Its  further  advantage 
of  changing  to  "star"  connection  at  some  future  time  in  case  it 
seems  desirable  to  raise  the  transmission  line  voltage  should  not 
be  neglected  in  making  a  decision. 

Table  IX  will  be  found  convenient  in  selecting  transformer 
voltages  for  converters  of  various  types.  This  table  is  based 
upon  600  volts  at  the  direct  current  side  of  the  machine  and  while 
it  represents  average  practice  it  must  be  remembered  that  the 
voltage  ratio  is  dependent  upon  the  design  of  machine  and  may 
therefore  vary  slightly  with  machines  of  different  manufacture. 

TABLE  IX. 
Voltage  Ratios  in  Synchroxous  Coxverters. 


Actual  ratio. 


Zero  load. 


Full  load  Full  load 

(straight).  (inverted). 


Theoretical 
ratio. 


Single  phase 429  435  423  424 

Three  phase 366  372  360  367 


In  many  substations  six-phase  synchronous  converters  will  be 
found  operating  upon  three-phase  transmission  systems.  This 
procedure  is  adopted  because  of  the  higher  efficiency  and  greater 
output  of  the  six-phase  machine  for  the  same  size  of  frame.  The 
connections  and  switching  apparatus  of  the  six-phase  converter 
are  necessarily  more  complicated  than  with  the  three-phase 
machine.  From  Table  X  which  illustrates  the  increased  capacity 
of  converters  of  different  phases  for  the  same  size  of  frame  it  will 
be  noted  that  a  six-phase  converter  has  nearly  double  the  capacity 


SUBSTATION    LOCATION    AND    DESIGN. 


II 


of  the  same  machine  operated  as  a  direct  current  generator  and 
nearly  one  and  one-half  times  that  of  a  three-phase  converter. 
If  a  sufficently  large  commutator  and  brush  rigging  be  provided 

wvvwvwv 

AAAA   AAAA     AAAA 


/  e  b 

Fig.  40. — Six-phase  "delta"  connections  from  three-phase  primaries. 
(Double  secondary  required.) 

on  a  three-phase  machine  rated  at  500  amperes,  it  may  be  used 
as  a  six-phase  machine,  if  properly  connected,  for  an  output  of 
725  amperes  with  the  same  temperature  rise. 


WV\AAAAAA/ 
AAAA 


ad  c  / 

Fig.  41. — Six-phase    "star"    connections    from    three-phase    primaries. 
(Double  secondary  required.) 

TABLE  X.^ 
CoMP.AR.^Tiv-E  Ratings  of  Coxverters. 


D.  c.  Single-phase        Three-phase  Two-phase  Six-phase 

generator.  converter.  converter.  converter.  converter. 


0.85 


1-32 


1.62 


1.92 


Elements  of  Electrical  Engineering,  Vol.  II,  Franklin  and  Esty. 


ii6 


ELECTRIC    RAILWAY    ENGINEERING. 


The  above  discussion  has  a  direct  bearing  upon  the  question 
of  transformer  connections,  for  if  a  six-phase  converter  be  in- 
stalled one  of  the  methods  of  connection  illustrated  in  Figs.  40, 
41,  and  42  must  be  adopted  if  the  three-phase  supply  is  to  be 
retained. 

Transformers  may  be  further  classified  with  regard  to  their 
method  of  cooling  as  follows: 

1.  Oil  cooled. 

2.  Air  cooled. 

3.  Water  cooled. 


Fig.  42. — Six-phase    diametrical    connections    from    three-phase    primaries. 
(Single  secondary  only.) 


Transformers  of  the  "  oil  cooled  "  class  depend  for  their  cooling 
upon  the  natural  circulation  of  a  comparatively  large  body  of 
oil  within  the  transformer  case,  all  the  heat  being  radiated  from 
the  surface  of  the  corrugated  iron  cases.  This  construction  is 
suitable  for  transformers  of  all  potentials  and  for  capacities  up 
to  500  kw. 

Air  cooled  transformers  are  cooled  by  means  of  an  air  blast 
provided  by  a  motor  driven  blower  and  forced  through  the  air 
ducts  of  the  transformer  core.     This  method  of  cooling  requires 


SUBSTATION    LOCATION   AND    DESIGN.  II 7 

the  construction  of  air  ducts  in  the  floor,  usually  of  concrete,  and 
involves  the  additional  cost  of  blower  outfits.  It  is  suitable  for 
all  capacities  but  is  limited  to  potentials  of  33,000  volts  or  less. 

Transformers  of  the  third  class  contain  a  series  of  pipe  coils 
within  the  case,  the  insulating  oil  circulating  around  the  coils 
while  the  latter  are  cooled  by  means  of  circulating  water  within. 
This  type  of  transformer  is  used  for  all  the  largest  installations 
and  is  not  limited  as  to  capacity  or  voltage. 

Compounding  Reactances. — One  of  the  disadvantages  of 
the  synchronous  converter  is  the  difficulty  of  compounding  the 
machine  for  constant  or  increasing  d.  c.  voltage  with  increase 
of  load.  This  difficulty  arises  from  the  fact  that  when  the  field 
strength  of  the  converter  is  varied  its  direct  current  voltage  is 
not  appreciably  changed.  The  converter  acts  as  a  synchronous 
motor  in  this  respect,  the  increase  of  field  strength  causing  the 
motor  to  draw  a  leading  current  from  the  line.  It  is  this  latter 
feature  that  makes  it  possible  to  compound  the  converter  if  an 
external  reactance  be  connected  in  series  with  each  of  the  phases 
between  the  transformers  and  the  converter.  If  the  machine  be 
designed  to  give  rated  voltage  at  a  light  load  with  the  reactance  in 
circuit,  it  follows  that  the  leading  current  produced  by  a  series 
field  as  the  load  increases  will  neutralize  the  inductive  voltage 
of  the  reactance  coil  and  thereby  impress  an  equal  or  even  higher 
voltage  on  the  converter  at  full  load.  As  there  is  a  fixed  ratio 
between  the  a.  c.  and  d.  c.  voltages,  the  latter  is  compounded  at 
the  same  time.  The  combination  of  series  field  and  external 
reactance  is  therefore  necessary  for  compounding  a  converter, 
whereas  the  former  only  is  required  for  the  d.  c.  generator  of  the 
motor  generator  set. 

Switchboard. — The  typical  substation  switchboard  consists  of 
the  following  classes  of  panels : 

1.  High  tension  line. 

2.  High  tension  transformer. 

3.  A.  c.  converter  or  motor  generator. 

4.  D.  c.  converter  or  motor  generator. 

5.  Totalizing. 

6.  D.  c.  feeder. 

The  number  of  panels  in  each  class  is  dependent  upon  the  size  of 


Il8  ELECTRIC    RAILWAY    ENGINEERING. 

Station  and  the  number  of  converters  it  contains  but  all  panels 
of  each  class  are  usually  grouped  by  themselves. 

The  two  classes  of  high  tension  panels  are  usually  of  the  remote 
control  type.  This  is  universally  the  case  above  13,000  volts. 
With  this  construction  the  high  tension  switches  are  mounted  in 
fire-proof  compartments  of  concrete,  tile,  or  brick  and  may  there- 
fore be  located  at  some  distance  from  the  control  board.  No  high 
tension  lines  are  connected  with  the  control  board,  the  switches 
being  operated  by  means  of  auxiliary  125  volt  d.  c.  circuits  and 
the  meters  connected  with  the  secondary  windings  of  current  and 
potential  transformers  whose  primary  windings  are  in  the  high 
tension  circuits.  Red  and  green  illuminated  bulls-eyes  on  the 
switchboard  panels  indicate  whether  the  main  switches  are  closed 
or  open  respectively. 

The  high  tension  line  switches  control  the  connections  between 
high  tension  lines  and  the  station  bus  bars,  while  each  bank  of 
transformers  is  connected  to  the  high  tension  buses  by  means  of 
the  switches  controlled  by  the  panels  of  the  second  group.  These 
latter  switches  and  often  both  groups  of  switches  are  provided 
with  inverse  time  limit  relays  which  act  as  circuit  breakers  in  case 
of  overload,  with  the  further  provision  that  they  may  be  adjusted 
to  operate  only  after  the  overload  has  continued  for  a  prearranged 
interval.  The  "inverse"  type  of  relay  is  in  addition  so  designed 
that  the  greater  the  overload,  the  shorter  will  be  the  time  in 
which  it  will  open.  With  the  transformer  relays  set  for  a  very 
short  interval,  the  high  tension  line  switches  arranged  so  as  to 
open  a  fraction  of  a  second  later  if  the  overload  still  continues 
and  with  the  relays  in  the  out-going  high  tension  feeders  at  the 
power  house  adjusted  for  an  interval  of  one  or  two  seconds,  it 
will  be  seen  that  only  those  switches  connecting  apparatus  or 
lines  upon  which  there  is  trouble  will  be  opened  and  the  inter- 
ference with  other  service  reduced  to  a  minimum. 

The  meters  to  be  installed  on  the  first  two  groups  of  panels 
often  vary  widely  with  the  personal  preference  of  the  engineer 
in  charge,  an  average  equipment  probably  consisting  of  an  am- 
meter in  each  phase,  a  power  factor  meter  and  a  voltmeter  on  a 
swinging  bracket  at  the  end  of  the  board. 

The  panels  of  group  three  contain  all  equipment  necessary  for 


SUBSTATION    LOCATION    AND    DESIGN. 


119 


the  control  of  the  a.  c.  side  of  the  converter  or  motor  generator 
as  the  case  may  be  and  usually  include  a  low  voltage  secondary 
a.  c.  switch  for  connecting  converter  to  transformers,  motor  field 
rheostat  in  case  of  a  synchronous  motor  generator  set,  starting 
switch  if  starting  motor  be  used,  together  with  synchronizing  and 
voltmeter  plugs.  The  instruments  usually  consist  of  three  am- 
meters and  a  power  factor  meter. 

The  direct  current  panels  perform  the  office  of  connecting  the 
direct  current  or  output  side  of  the  converter  or  motor  generator  to 


Fig.  4j. 


the  direct  current  bus  bars.  For  this  function  three  single  pole 
switches  are  usually  employed,  one  positive,  one  negative,  and  an 
equalizer  switch.  The  negative  and  equalizer  switches  are  often 
located  on  a  pedestal  or  on  the  frame  of  the  converter  thereby 
simplifying  the  switchboard  connections.  The  field  rheostat  con- 
trol of  the  converter  or  of  the  generator  of  the  motor  generator 
set  is  located  on  this  panel  together  with  a  circuit  breaker,  a  d.  c. 
potential  receptacle,  and  a  starting  switch  in  case  it  is  planned  to 
start  the  machine  from  the  d.  c.  side.  The  meters  are  usually 
confined  to  a  main  ammeter  and  indicating  wattmeter  with  a  d.  c. 
voltmeter  on  a  swinging  bracket.  In  large  installations  a  field 
ammeter  is  often  included  on  this  panel. 


I20 


ELECTRIC   RAILWAY   ENGINEERING. 


The  totalizing  panel  contains  instruments  only  and  these  are 
so  connected  as  to  measure  the  total  output  of  the  station  between 
the  d.  c.  converter  panels  and  the  outgoing  feeders.  An  ammeter 
or  indicating  wattmeter  and  an  integrating  wattmeter  are 
usually  installed.  This  panel  is  often  entirely  omitted  and  the 
latter  instrument  mounted  on  the  sub-base  of  one  of  the  other 
panels. 

The  out-going  feeder  panels  may  be  designed  to  control  one 
or  two  feeders  each.  Single  pole  (positive)  switches  and  circuit 
breakers  in  series  with  ammeters  make  up  the  usual  equipment 
for  each  feeder. 


Fig.  44. 


The  entire  board  is  usually  of  the  standard  size  90  in. 
in  height  including  a  28-in.  sub-base  with  panels  varying  in 
width  from  16  to  36  in.  Blue  Vermont  marble  forms  the 
principal  material  of  construction  although  low  voltage  boards  are 
often  built  of  slate.  The  board  should  be  spaced  at  least  4  ft. 
from  the  wall  and  the  wiring  at  the  back  should  be  generously 
lighted.  Where  gallery  boards  of  the  remote  control  type  are 
installed  from  which  the  operator  may  view  all  the  machines 


SUBSTATION    LOCATION   AND    DESIGN. 


121 


under  his  control,  the  "desk  type"  of  board  has  been  quite 
frequently  specified.  In  Figs.  43  and  44  will  be  found  views  of 
typical  railway  substation  switchboards. 

Storage  Battery  Auxiliary. — While  the  storage  battery  is 
looked  upon  by  many  engineers  and  managers  as  an  evil  to  be 
avoided,  it  certainly  has  its  important  place  in  the  substation 
equipment  of  many  roads.  Its  possible  function  is  three-fold, 
although  it  is  often  installed  for  the  purpose  of  meeting  but  one  of 
the  following  requirements: 

1.  To  aid  in  maintaining  constant  potential. 

2.  To  supply  all  peak  loads  above  a  certain  predetermined 
average. 

3.  To  assume  the  entire  load  of  the  substation  for  a  short 
period  of  time. 


Fig.  45- 


When  the  second  and  third  functions  listed  above  are  assumed 
by  the  battery,  its  capacity  must  be  rapidly  increased,  yet  in 
many  instances  batteries  of  sufficient  capacity  to  fill  these  three 
requisites  are  maintained  in  practically  all  substations  of  the 
road. 

As  the  maintenance  and  depreciation  of  a  battery  is  relatively 
high,  the  local  problem  must  be  carefully  studied  before  a  decision 
can  be  reached.  Such  a  study  should  balance  the  fixed  charges  of 
the  battery  and  accompanying  control  equipment  combined  with 


122 


ELECTRIC    R.\ILWAY    ENGINEERING. 


its  maintenance,  against  the  fixed  charges  of  the  relay  equipment 
and  the  extra  line  copper  that  would  otherwise  have  to  be  installed, 
plus  the  rather  intangible  factors  of  irregular  schedule  due  to 
variable  voltage  and  total  interruption  to  service. 

Arrangement  of  Apparatus. — There  is  little  variation  in  the 
arrangement  of  apparatus  in  a  railway  substation  except  in  the 
extreme  cases  where  it  is  necessary  to  locate  the  equipment  on 


Fig.  46. 


two  floors.  The  high  tension  apparatus  is  usually  confined  to  a 
separate  room  and  is  often  located  in  fire-proof  vaults.  The 
converters,  reactances,  and  switchboard  are  usually  located  very 
close  together  in  a  single  room  with  the  wiring  either  in  conduit 
embedded  in  the  floor  or  of  the  open  type  supported  from  insulator 
racks  on  the  basement  ceiling.  The  principal  features  which  tend 
materially  to  alter  the  design  of  a  substation  are  the  overhead  or 
underground  entrances  of  high  tension  and  d.  c.  feeder  cables. 


SUBSTATION    LOCATION   AND    DESIGN. 


123 


Typical  stations  involving  each  type  of  construction  are  illustrated 
in  Figs.  45  and  46. 

Wiring. — The  wiring  of  the  station  is  usually  figured  from  the 
standpoint  of  carrying  capacity  only,  as  the  potential  drop  for 
the  short  distances  involved  is  generally  negligible.  The  resist- 
ances of  the  d.  c.  cables  between  converter  and  switchboard 
should,  however,  be  carefully  balanced  in  order  to  divide  the 
load  properly  between  two  or  more  machines  operating  in  parallel. 


Fig.  47- 


The  low  tension  wiring  and  the  high  tension  cables  up  to  13,000 
volts  are  usually  insulated  with  rubber,  paper,  or  varnished 
cambric  and  protected  either  with  braid  or  a  lead  sheath.  Such 
construction  is  well  illustrated  in  Fig.  47,  while  a  simplified  wiring 
diagram  for  a  typical  substation  will  be  found  in  Fig.  48.  Wiring 
above  13,000  volts,  and  often  that  at  lower  voltage  is  carried  on 
line  type  insulators  with  no  further  insulation,  these  lines  often 
being  run  in  individual  concrete  or  brick  compartments  with  con- 


124 


ELECTRIC    RAILWAY   ENGINEERING. 


'^  (^|{fvljvvwvv| 


SUBSTATION    LOCATION   AND    DESIGN. 


125 


venient  chambers  provided  for  sectionalizing  or  disconnecting 
switches  and  instrument  transformers. 

Lightning  Protection. — The  incoming  high  tension  lines  and 
the  outgoing  railway  feeders  are  each  provided,  just  within  the 
wall  of  the  station,  with  a  helix  of  wire  of  the  same  size  as  the  line 
wire  which  acts  as  a  "choke  coil"  to  divert  high  frequency  surges 
to  the  lightning  arresters  connected  between  the  coils  and  the 


Fig.  49. 

outside  lines.  These  arresters  which  will  be  found  described  at 
length  in  manufacturers'  bulletins  usually  comprise  a  series  of 
spark  gaps  between  the  lines  and  ground  which  will  permit  a 
discharge  to  pass  when  an  excessive  voltage  occurs  and  yet  quench 
the  arc  which  would  otherwise  follow  over  the  gaps  when  supplied 
with  normal  line  potential.  The  recent  type  of  electrolytic 
arrester,  Fig.  49,  however,  interposes  a  series  of  liquid  films  of 
high  resistance  in  place  of  the  spark  gaps  and  is  therefore  self 


126 


ELECTRIC    RAILWAY    ENGINEERING. 


healing.  Two  objectionable  features  of  this  arrester,  however, 
are  its  tendency  to  freeze  in  cold  weather  and  the  necessity  of 
"charging"  it  from  time  to  time  to  maintain  the  films  of  electrolyte 
in  working  order. 

Portable    Substations. — On    many    roads    traffic    demands 
become  excessive  upon  certain  days  or  weeks  of  the  year  on  differ- 


Fiu.   50. 


ent  sections  of  the  line.  A  means  of  meeting  this  local  and 
temporary  demand  for  power  has  been  found  in  the  "portable 
substation,"  Fig.  50,  which  usually  consists  of  a  box  car  with  a 
converter,  transformers,  switchboard,  etc.,  complete  and  ready 
for  connection  to  the  high  tension  lines  at  any  point  on  the 
system  and  capable  of  operating  in  parallel  with  the  permanent 
station  on  any  desired  trolley  section.    Such  a  portable  station  has 


SUBSTATION    LOCATION   AND    DESIGN. 


127 


proved  a  means  of  providing  good  service  under  extreme  con- 
ditions not  only,  but  has  protected  the  regular  equipment  from 
damage  due  to  serious  overload  as  well. 

High  Voltage  Direct  Current  Substations.— Within  the  last 
few  years  the  1200  A'olt  direct  current  railway  system  has  been 
developed  and  some  dozen  interurban  roads  are  now  operating 
on  this  voltage.  This  increase  of  voltage  decreases  the  first 
cost  of  installation  as  it  reduces  the  number  of  substations  neces- 
sary as  well  as  the  amount  of  distribution  copper  required.  A 
more  detailed  cofnparison  of  its  cost  and  advantages  will  be 
found  in  a  later  chapter. 


The  substation  design  for  such  a  system  is  not  materially 
different  from  that  outlined  above  except  in  the  case  of  the  con- 
verting equipment.  Two  standard  600  volt  machines,  connected 
in  series,  are  usually  installed  for  this  service,  the  negative  terminal 
of  one  unit  being  connected  to  the  rail  while  the  positive  lead  from 
the  second  machine  is  carried  to  the  switchboard  bus  bars  and 
thence  through  1200  volt  feeder  panels  to  the  feeders  and  trolley. 
Fig.  51  shows  the  synchronous  motor  generator  set  used  for  such 
service  in  the  substation  of  the  Pittsburg,  Harmony,  Butler,  and 
New  Castle  Railway  while  the  wiring  diagram  for  this  station 
will  be  found  in  Fig.  52.  It  should  be  noted  that  in  this  in- 
stallation no  transformers  are  used  although  the  synchronous 
motor  of  the  motor  generator  set  operates  at  13,200  volts. 


128 


ELECTRIC   RAILWAY   ENGINEERING. 


Single-phase  Alternating  Current  Substations. — In  systems 
where  single-phase  alternating  current  is  supplied  to  the  car  in 
place  of  direct  current  there  is,  of  course,  no  demand  for  the 
conversion  of  alternating  current  to  direct  current  in  the  sub- 
station.    On  long  lines,  however,  substations  are  still  necessary 


C.D.G. 
'  A  T  V    Pa°e'g    125  V.D.C.  6  Kw  13200  V.A.C. 
400  Kw. 

lucoming  Lines 


Exciter 

SynchroQoua 
Motor 

^—-  Bus  (.Gfrouuded) 
■  Kqualizer 

Fig.  52. 

to  reduce  the  potential  of  the  transmission  line  to  that  suitable 
for  the  trolley,  the  latter  voltage  usually  being  6,600  or  13,000 
volts.  Such  substations  involving  only  transformers,  lightning 
protection,  and  switches,  require  no  attendants  and  are  therefore 
very  small  and  simple  in  design  as  compared  with  the  stations 


SUBSTATION    LOCATION   AND    DESIGN. 


129 


previously  considered.  Automatic  oil  switches  are  usually 
installed  in  both  primary  and  secondary  circuits  of  the  step-down 
transformers  although  in  this  case  the  time  element  of  the  auto- 
matic relay  is  adjusted  for  a  greater  time  interval  than  those  at 
the  power  station  in  order  that  the  latter  switches  will  open  first 
in  case  of  trouble.  This  method,  which  is  just  the  reverse  of  that 
in  converter  substations,  is  adopted  to  avoid  frequent  trips  to  the 


t'lG-  53- 


substation  to  close  switches.  The  accompanying  Fig.  53  illus- 
trates one  of  the  stations  of  this  type  on  the  Chicago,  Lake  Shore, 
and  South  Bend  Railway  which  is  probably  the  longest  interurban 
system  operating  single-phase  in  this  country. 

Substation  Cost. — The  following  working  estimate  prepared 
to  cover  the  total  cost  of  four  substations  of  the  600  volt  direct 
current  type  for  a  63-mile  interurban  line  in  the  South  may  be 
useful  in  determining  the  relative  cost  of  substation  equipment. 
As  each  station  contains  one  synchronous  converter  of  300  kw., 
the  costs  may  be  figured  on  a  basis  of  300  kw.  per  station. 
9 


130  ELECTRIC    RAILWAY    ENGINEERING. 

4  Substation  iDuildings,  @,$4.oo  kw $4,800 

4  Converter  foundations,  150  yd.  @  $8.00  1,200 

4  Transformer  banks,  1320  kw.  @  $10.00 i3>20o 

4  Converters,  1200  kw.  @,  $16.00 19,200 

Freight  and  erection, 3, 000 

4  Switchboards,  4  panels  each 8,800 

Freight  and  erection 1,600 

Wiring,  @  $1.50  per  kw 1,800 

High  tension  switch  cells 1,000 

Lightning  protection 2,400 

Total.  @  $47.50  kw $57,000 

Whereas  the  discussion  in  this  chapter  covers  the  principal 
features  of  substation  location  and  design,  many  special  features 
with  regard  to  operating  costs  and  the  function  which  the  sub- 
station has  to  play  in  the  various  types  of  distribution  systems 
will  be  considered  briefly  in  succeeding  chapters. 


CHAPTER  IV. 

Transmission  System. 

The  necessity  for  greatly  detailed  calculations  in  designing 
high  tension  transmission  lines  for  railway  systems  is  often  ex- 
aggerated. The  fact  that  the  careful  predetermination  of  all 
characteristics  of  such  a  transmission  line  is  unnecessary,  when 
compared  with  the  careful  study  required  in  connection  with  a 
line  for  the  transmission  of  power  for  lighting  or  even  for  the  very 
high  voltage  long  distance  transmission  of  energy  in  large  quan- 
tities from  hydro-electric  plants,  will  be  made  clear  by  the  following 
outline  of  conditions  generally  pertaining  to  the  railway  system. 

In  the  first  place  the  close  regulation  of  voltage  is  both  un- 
necessary and  impossible.  The  sudden  variations  of  power  de- 
manded by  cars,  especially  upon  an  interurban  system,  must 
inevitably  mean  variable  voltage  and  with  such  voltage  variation 
on  the  distribution  system  there  is  little  need  of  the  closest  possible 
regulation  on  the  transmission  line. 

Nor  is  the  service  impaired  by  such  voltage  variation  as  would 
be  suicidal  to  the  lighting  substation.  The  motorman  or  pass- 
engers upon  an  interurban  car  will  hardly  notice  a  ten  per  cent, 
voltage  variation,  while  sudden  variations  of  2  or  3  per  cent,  are 
to  be  avoided  if  possible  in  connection  with  incandescent  lighting, 
particularly  as  the  intensity  of  light  varies  throughout  a  greater 
range  than  the  voltage.  The  lighting  of  interurban  cars  is  of 
course  greatly  impaired  by  poor  voltage  regulation  and  this  is 
one  of  the  features  that  is  receiving  a  great  deal  of  just  criticism 
from  the  traveling  public.  Its  remedy,  however,  lies  in  making 
the  lighting  independent  of  trolley  voltage  and  not  by  attempting 
to  regulate  the  latter  more  closely. 

The  regulation  of  transmission  lines  is  greatly  affected  by  low 
power  factor.  The  addition  of  induction  motors  or  arc  lighting 
systems  which  operate  at  low  power  factors  to  long  distance 
transmission  lines  involves  very  careful  design  and  costly  reg- 
ulating apparatus  if  lighting  loads  are  to  be  successfully  supplied 
by  the  same  line.  Jn  many  such  instances  synchronous  motors 
are  installed,  often  without  direct  financial  return  to  the  company, 

131 


132  ELECTRIC    RAILWAY   ENGINEERING. 

in  order  that  the  power  factor  may  be  properly  controlled.  Such 
control  is  present  in  the  railway  substation  in  either  the  synchro- 
nous motor  generator  set  or  converter  and  with  little  practice  the 
substation  attendant  can  maintain  very  nearly  unity  power  factor 
on  the  transmission  line  and  thereby  aid  its  regulation  to  a  great 
extent. 

Many  of  the  limiting  factors  in  high  tension  line  design  such 
as  the  pin  type  of  insulator,  corona  losses,  troubles  introduced  by 
wide  spacing  and  long  spans,  etc.,  are  introduced  only  when  the 
voltage  becomes  higher  and  the  amounts  of  power  become  much 
greater  than  those  involved  in  the  major  part  of  the  interurban 
transmission.  In  fact  a  census  of  transmission  lines  for  railway 
purposes  only  would  probably  reveal  the  fact  that  an  extremely 
small  percentage  of  these  lines  are  above  33,000  volts.  At  this 
voltage  two  parallel  three-phase  circuits  on  pin  type  insulators 
and  wooden  poles  carrying  in  addition  the  distribution  feeders 
and  trolley  brackets  represent  common  practice.  Such  a  line  in 
the  Middle  West  has  for  years  been  satisfactorily  operating  an 
interurban  system  no  miles  in  length  at  33,000  volts.  In  such 
design  simple  electrical  and  mechanical  considerations  are  alone 
involved. 

For  the  above  reasons,  therefore,  and  because  of  the  very  able 
treatises  in  complete  volumes  devoted  to  the  details  of  this  subject, 
an  exhaustive  study  of  transmission  line  design  will  not  be  at- 
tempted in  these  pages. 

The  three-phase  system  of  alternating  current  transmission 
has  been  standardized  almost  exclusively  for  railway  work.  This 
is  principally  because  polyphase  apparatus  is  necessary  for  sub- 
station units  in  large  sizes  and  in  addition  because  the  three-phase 
system  requires  but  three-fourths  the  copper  of  the  single-phase 
installation.  Other  polyphase  systems,  although  more  economical 
in  copper  in  some  instances,  have  not  found  favor  largely  because 
of  the  complication  introduced  by  the  greater  number  of  wires. 
While  six-phase  substation  apparatus  was  shown  in  the  preceding 
chapter  to  be  highly  desirable,  the  possibility  of  its  operation  from 
a  three-phase  line  has  introduced  no  serious  consideration  of 
six-phase  transmission.  For  these  reasons,  therefore,  three-phase 
transmission  onlv  will  be  herein  considered. 


TRANSMISSION    SYSTEM.  1 33 

Mechanical  Strength. — Owing  to  the  fact  that  calculations 
of  the  proper  size  of  wire  for  transmission  lines  based  on  Kelvin's 
law,  voltage  regulation,  and  carrying  capacity,  in  most  cases 
result  in  a  wire  too  small  to  withstand  the  mechanical  stresses 
incurred  by  ordinary  line  construction  and  weather  conditions, 
the  mechanical  strength  of  the  line  may  well  be  considered  first 
and  the  size  of  wire  checked  in  accordance  with  the  electrical 
considerations  later.  No  wires  smaller  than  No.  4  B.  &  S. 
hard  drawn  copper  or  its  equivalent  in  tensile  strength  should 
be  used  for  mechanical  reasons.  If  aluminum  be  used  it  should 
be  remembered  that  for  the  same  size  aluminum  weighs  about 
30  per  cent,  and  has  a  resistance  of  i .  67  times  that  of  hard  drawn 
copper.  Aluminum  costs  considerably  less  than  copper  for  the 
same  conductivity  and  melts  at  a  much  lower  temperature.  It 
also  has  a  greater  coefficient  of  expansion  causing  greater  vari- 
ation in  sag  with  change  of  temperature.  It  is  difficult  to  solder, 
is  quickly  attacked  by  gases  in  the  atmosphere  and  has  a  tensile 
strength  of  approximately  one-third  that  of  copper.  In  spite 
of  its  many  disadvantages  aluminum  is  used  to  a  considerable 
extent  for  line  construction  largely  because  of  its  low  cost  and 
light  weight.  Joints  are  made  mechanically  by  overlapping  the 
ends  in  an  oval  sleeve  and  twisting  the  sleeve  and  wire  ends  to- 
gether without  solder.  On  account  of  its  large  diameter  for  a 
given  conductivity  the  total  wind  pressure  on  a  line  is  greater  and 
because  of  its  low  melting  point  it  is  more  likely  to  melt  apart 
than  is  copper  in  the  event  of  an  arc  forming  between  wires. 

The  question  whether  one  or  two  parallel  three-phase  lines 
shall  be  installed,  one  for  the  purpose  of  acting  as  a  relay  for 
the  other  in  case  of  break-down  is  an  open  one  and  is  generally 
decided  by  the  personal  preference  of  the  engineer  in  charge.  If 
a  single  line  only  be  installed  it  is  usually  mechanically  stronger 
and  therefore  better  able  to  withstand  abnormal  strains.  In 
this  case  the  wires  are  spaced  at  the  vertices  of  an  equilateral  tri- 
angle with  one  wire  on  the  pole  top  and  the  two  lower  wires  on  a 
single  cross  arm.  If  two  circuits  are  employed  two  arms  are  used 
and  one  circuit  is  installed  on  either  side  of  the  pole.  Such  con- 
struction permits  repairs  to  be  made  on  one  of  the  lines  with  the 
other  in  operation  when  the  voltage  does  not  exceed  33,000  volts. 


134  ELECTRIC    RAILWAY   ENGINEERING. 

No  particular  specifications  need  be  made  for  the  poles,  which 
are  also  used  for  the  trolley  span  wires,  feeders,  and  probably 
signal  and  telephone  circuits  as  well,  except  that  they  must  be 
sufficiently  high  to  give  sufficient  clearance  to  the  high  tension 
wires  during  the  period  of  maximum  sag  and  that  they  be  at  least 
7  in.  in  diameter  at  the  top.  The  forces  acting  on  the  poles 
due  to  the  presence  of  the  high  tension  line  are, 

Vertical  downward  force  due  to  weight  of  conductors  with 

possible  ice  sheath, and  vertical  component  of  wire  tension. 

Bending  moment  due  to  angle  in  line  or  with  one  or  more 

wires  broken. 

Bending  moment  due  to  wind  pressure  on  pole  and   ice 

sheathed  wires. 
Although  these  forces  may  be  readily  calculated  by  means  of  the 
fundamental  laws  of  mechanics,  it  is  safe  to  assume  that  there  is 
a  sufficient  factor  of  safety  with  a  properly  constructed  pole  line 
sufficiently  heavy  for  the  trolley  and  feeder  installation  for  the 
reason  that  the  latter  acts  as  a  longitudinal  anchor  guy  in  case 
of  a  broken  high  tension  wire  and  owing  to  the  further  fact  that 
the  possible  strains  on  the  high  tension  line  are  generally  small 
as  compared  with  those  incurred  by  the  feeder  and  trolley 
construction. 

Electrical  Considerations. — Considering  the  large  number 
of  railway  high  tension  lines  using  No.  4  B.  &  S.  wire,  and 
remembering  that  this  should  be  a  minimum  for  mechanical 
reasons,  it  will  probably  save  time  in  calculation  to  assume  this 
size  at  the  start.  A  convenient  spacing  for  wires  not  exceeding 
33,000  volts  is  36  in.  With  these  dimensions  in  mind  it 
will  be  remembered  that  in  determining  the  regulation  of  an 
alternating  current  line  the  impedance  must  be  considered  in 
place  of  the  resistance  which  is  used  in  direct  current  calculations. 
Impedance  may  be  considered  as  the  resultant  of  the  resistance 
and  the  reactance  of  the  line  combined  at  right  angles.  In  other 
words, 

Z  =  \/R'+X'  (81) 

where  Z  =  Impedance  of  line  in  ohms. 
R  =  Resistance  of  line  in  ohms. 
X  =  Reactance  of  line  in  ohms. 


TR,\XSMISSIOX    SYSTEM.  1 35 

The  reactance  (X)  of  a  transmission  line  is  partly  due  to  in- 
ductance (L),  which  in  turn  is  dependent  upon  the  cutting  by 
the  wire  of  lines  of  force  set  up  by  the  current  in  the  wire,  and  the 
capacity  (C)  which  is  the  effect  due  to  the  wires  acting  as  the 
plates  of  condensers  with  the  air  as  a  dielectric  medium  between. 
Since  the  formulae  for  these  quantities  given  below  show  that  the 
capacity  is  decreased  and  the  inductance  increased  as  the  wires 
are  moved  apart  and  also  as  the  size  of  wire  is  decreased,  these 
two  functions  of  reactance  will  be  seen  to  be  opposed  to  one 
another,  one  neutralizing  the  other  to  some  extent.  Since  the 
capacity  effect  is  relatively  small,  especially  on  the  average  short 
line  of  the  interurban  railway  operating  at  moderate  voltage,  it 
will  be  neglected  in  the  first  determination  of  regulation  and  the 
error  introduced  by  such  a  procedure  pointed  out  later. 

As  the  theoretical  proof  of  the  formulae  for  line  inductance  and 
capacity  is  beyond  the  scope  of  this  book  and  as  their  methods 
of  derivation  are  included  in  most  theoretical  treatises  on  electri- 
cal engineering  they  are  listed  below  without  proof. 

0.0776  1 
C=        "    ^  (82) 

2  log.  10  J. 

/  d  \ 
L  =.000322 (2. 303  log^ol^  ^  j +0.25)1  (83) 

where  L  =  Self  inductance  per  wire  in  henries. 

d  =  Distance  between  wire  centers  in  inches. 
r  =  Radius  of  wire  in  inches. 

C  =  Capacity  between  one  wire  and  neutral  point  in  micro- 
farads. 
1  =  Length  of  circuit  in  miles. 
Considering  only  the  resistance  and  inductive  reactance  of  the 
line  at  present  the  latter  may  be  found  from  the  equation, 

X,=  2-fL.  (84) 

where    Xl  =  Reactance  due  to  inductance  in  ohms. 
f  =  Frequency  in  cycles  per  sec. 
L  =  Inductance  from  equation  (83)  in  henries. 
Tables  giving  such  of  the  inductive  reactance  values  and  re- 
sistances as  will  be  needed  in  railway  transmission  line  calcu- 
lations are  given  below. 


136 


ELECTRIC    RAILWAY    ENGINEERING. 


TABLE  XI.i 
Inductive  Reactance  of  Single  Wire  in  Ohms  per  Mile. 


Size  wire. 

Spacing  inches  25  cycles. 

24 

36 

48 

60 

72        84 

96 

108 

120 

150 

350000  cm. 

300000 

250000 

4/0  B  &  S 

3/0 

2/0 

0 

I 

2 

3 

4 

6 

•235 
■238 
.242 
.248 
•254 
•259 
.265 
.271 

•277 
•283 
.289 
.300 

•255 
.258 
•263 
.268 
•274 
.280 
.286 
.292 
.297 
•303 
■309 
.321 

.270 

•273 
.278 
.283 
.289 
.294 
.300 
.306 
.312 
.318 
•324 
•335 

.280 
.285 
.289 
.294 
.300 
.306 

•311 
.318 
•323 
•329 
•335 
•347 

! 
.290 

•  294 
.298 

•303 

•  309 
•315 
.321 

■327 

•  332 
■338 
■  344 
■356 

.298 
.301 

•305 
.310 

■317 
•323 
•329 
•334 
•  340 
■345 
•352 
•363 

•  304 
.308 

■3^3 
.318 

•  324 
•329 
•335 
•341 
•347 
•352 

•359 
•370 

.310 

•314 

■319 

•325 

•330 

•335 

•341 

•347  . 

■353 

•359 

•365 

•376 

•315 
.320 

■324 
•329 
•335 
•341 
•347 
•352 
•358 
•364 
•370 
.381 

•327 
•330 
•335 
■340 
•346 
•352 
■358 
•364 
•370 
•375 
.381 
•393 

TABLE  XII.  1 

Resistance  of  Copper  and  Aluminum  at  70^  Fahr. 


Size  wire. 

Ohms  per  mile. 

Copper. 

Alumimim. 

500000  cm. 

.109 

.176 

450000 

.121 

.196 

400000 

•137 

.221 

350000 

.156 

•  252 

300000 

.182 

.294 

250000 

.219 

•353 

4/0  B  &  S 

.258 

.417 

3/0 

.326 

.526 

2/0 

.411 

.664 

0 

.518 

•837 

I 

.653 

1-055 

2 

.824 

I  •330 

3 

1.039 

1.678 

4 

1.309 

2. 116 

6 

2.082 

3^309 

'Standard  Handbook,  Section  11,  p.  40. 


TRANSMISSION    SYSTEM.  I37 

Since  the  power  factor  at  the  substation  may  be  maintained 
at  approximately  loo  per  cent,  by  control  of  the  field  of  the 
synchronous  converter  or  motor  generator,  such  a  power  factor 
may  be  safely  assumed  in  line  calculation.  In  fact  it  would  not 
introduce  a  serious  error  to  neglect  impedance  of  the  line  entirely 
and  solve  the  problem  as  if  for  a  direct  current  system  since  even 
the  effect  of  line  reactance  may  be  overcome  by  careful  regulation 
of  the  substation  apparatus  as  explained  above. 

Voltage  Determination. — The  voltage  and  current  per  wire 
must  now  be  determined.  They  are  principally  dependent  upon 
the  substation  input  and  distance  of  transmission. 

In  deciding  upon  the  proper  voltage  for  the  transmission  line 
as  well  as  in  selecting  electrical  equipment  it  is  necessary  to  take 
into  consideration  the  standards  established  by  the  manufacturers. 
Primary  substation  voltages  have  been  standardized  as  follows: 
11,000,  19,100,  33,000,  and  66,000  volts.  The  two  lower  potentials 
are  most  often  used  with  ''delta"  connections  while  voltages  of 
33,000  and  66,000  are  obtained  with  "Star"  connected  trans- 
formers. It  should  be  noted  that  the  three  low^r  voltages  bear 
the  ratio  of  \/3  to  one  another  thus  permitting  the  next  higher 
standard  voltage  to  be  obtained  by  changing  connections  of  trans- 
formers from  "delta"  to  "star."  For  a  rough  selection  of  the 
voltage  to  be  first  used  for  calculation,  looo  volts  per  mile  of  trans- 
mission are  often  used.  As  local  conditions  enter  into  the  problem 
to  a  marked  degree,  and  since  it  is  almost  impossible  to  express 
intelligently  in  equation  form  all  the  factors  entering  into  the 
selection  of  the  proper  voltage  from  the  standpoint  of  regulation, 
first  cost,  and  economical  operation,  it  seems  advisable  to  select  two 
of  the  nearest  standard  voltages  by  the  above  rule  and  compare 
the  resulting  calculated  data  of  the  two  cases  before  finally 
determining  upon  the  best  operating  voltage. 

Regulation. — The  transmission  line  calculations  are  usually 
based  upon  the  combined  substation  inputs  supplied  by  a  single 
line  at  full  rated  load  although,  if  the  number  of  substations  be 
large,  it  may  be  found  from  a  study  of  their  load  curves  that  their 
maximum  loads  do  not  occur  simultaneously  and  that  the  total 
demand  on  the  transmission  line  may  be  considerably  below  the 
summation  of  the  substation  ratings.     The  rated  output  of  the 


138  ELECTRIC    RAILWAY    ENGINEERING. 

substation  transformers  was  found  in  Chapter  III  equation  (80). 
The  input  to  the  station  may  be  obtained  from  the  above  by 
dividing  the  output  of  all  transformers  by  the  transformer  effi- 
ciency which  may  be  safely  assumed  for  large  transformers  at 
full  load  as  98  per  cent. 

The  current  per  wire  on  the  transmission  line  is  therefore 

Kw.  X  1000 

V 3  E  cos  0 
where  I^,  =  Current  per  wire  in  amperes. 
Kw  =  Substation  input  in  kilowatts. 
E  =  Voltage  between  wires  at  substation, 
cos  0  =  Power  factor  of  load  at  substation. 
For  this  calculation  (cos  (fi)  is  taken  as  unity  as  explained  above. 


E«  l,..R 

Fig.  54. — ^Vector  diagram  for  transmission  line  regulation  unity  power  factor. 

The  impedance  of  the  transmission  line  may  now  be  found 
from  equation  (81)  if  values  of  reactance  and  resistance  from 
Tables  XI  and  XII  for  No.  4  B  &  S  wires  spaced  36  in.  apart 
be  substituted.     The  voltage  drop  on  the  line  is 

e  =  I^Z  (86) 

These  relations  including  the  generator  voltage  (E^)  are  shown 
in  Fig.  54  from  which  the  value  of  Eg  may  be  derived. 


E,=V(E3+iwR)H(i,.xj^  m 

where    (EJ    represents    substation    voltage    between    wire    and 

E 

neutral  or 

V3 

Reg  =  ^^^^  (88) 

If  less  than  unity  lagging  power  factor  be  assumed  as  in 
the  case  of  an  induction  motor  generator  set  for  example,  other 
conditions  remaining  the  same,  a  larger  current  (I'^)  would  have 


TRANSMISSIOxN    SYSTEM. 


^39 


resulted  from  equation  (85)  and  the  voltage  diagram  would  appear 
as  in  Fig.  55,  the  resulting  generator  voltage  being 

E',  =  v/(Es  cos^'r^'Ry^+^sin'^+Y'^^  (89) 
As  before,  the  percentage  regulation  may  be  obtained  from  the 
equation 

Reg'  =  ^'^~^^  (90) 

If  the  regulation  from  either  equation  (88)  or  (90)  is  unreason- 
ably high,  a  suitable  value,  say  10  per  cent.,  may  be  substituted 
back  into  the  equation  and  corresponding  values  of  Eg  or  E'g  found 


l«.Xi 


E^Cos  0 
Fig.  55. — Vector  diagram  for  transmission  line  regulation 


;ing  power  factor. 


from  which  the  correct  value  of  (R)  may  be  calculated  by  means  of 
equation  (87)  or  (89)  and  the  proper  size  of  wire  obtained  from  the 
wire  table. 

As  a  concrete  illustration  of  these  two  approximate  methods  of 
obtaining  regulation,  assume  the  following  conditions, 

Substation  input  =  1500  kilowatts. 

Power  factor       =  100  per  cent. 

Length  of  line     =  50  miles. 
Using  No.  4  wire  and  a  substation  voltage  of  33,000,  there  results, 

R  =  1.309  X  50  =  65.4  ohms. 

Xi.=o.3i  X  50   =15.5  ohms. 

33000 
Eg  per  terminal  =  —  ,     =19,100  volts 
V3 

Z  =  V'(65-4)H(i5-5)'  =  ^>7ohms. 

1,500,000 

I^  = -7^  =26.2  amp. 

33, 000  \/3 


E  =\/(i9,ioo-|-26.2x65.4)^+  (26.2  x  15. 5)'  =  20,820    (87) 


I40  ELECTRIC    RAIL^\^Y   ENGINEERING. 

20,820—19,100 

Reg  = =  9  per  cent.  (88) 

19,100 

Now  suppose  the  power  factor  to  be  lowered  to  85  per  cent,  by 

low  field  excitation  of  synchronous  apparatus  or  the  operation  of 

an  induction  motor  generator  set. 

1,500,000 

I'w  = -T' ^=30- 9  amp.  (85) 

33,000  Vs  X0.85 


E'g=\/(i9.ioox  .85  +  30.9  X  65.4)^(19,100x0.527  + 

309  X  i5-5)'  =  209oo  (89) 

20,900— 19,100 

Reg'  = =  9-43  per  cent.  (90) 

19,100 

Both  the  regulation  for  85  per  cent,  power  factor  and  unity 
power  factor  are  sufficiently  small  for  railway  service  and  the 
conditions  of  size  of  wire,  voltage,  spacing,  etc.,  may  be  tentatively 
decided  upon  and  checked  further  with  regard  to  Kelvin's  law, 
carrying  capacity,  etc.,  as  explained  under  "  Distribution  System." 

Capacity  Effect. — Since,  however,  the  capacity  has  been 
entirely  neglected  in  the  above  calculations,  the  error  introduced 
by  such  omission  should  at  least  be  pointed  out. 

As  previously  explained,  the  line  wires  act  as  plates  of  a  con- 
denser and  thus  draw  a  leading  "charging"  current  from  the 
power  house  just  as  an  infinite  number  of  small  condensers  would 
do  if  connected  in  parallel  across  the  line  wires  throughout  their 
entire  length.  As  such  a  uniform  distribution  of  capacity  involves 
a  constantly  changing  charging  current,  power  factor,  and  voltage 
throughout  the  entire  length  of  the  line,  which  condition  can  be 
represented  only  by  a  rather  involved  mathematical  equation,  it 
has  been  shown  by  Steinmetz^  that  this  capacity  effect  may  be  rep- 
resented sufficiently  accurately  by  locating  one-sixth  of  the  total 
capacity  at  either  end  and  two-thirds  in  the  middle  of  the  line. 
In  fact,  little  error  is  introduced  if  the  entire  capacity  is  con- 
sidered in  parallel  with  the  line  at  either  the  generator  or 
receiver  end.  Adopting  the  latter  assumption  the  equations 
below  show  the  method  of  derivation  of  the  values  in  Table  XI 
and  the  calculation  of  charging  current  for  any  assumed  length  of 
line,  voltage,  and  wire  spacing. 

^  Alternating  Current  Phenomena  by  Dr.  C.  P.  Steinmetz. 


TRANSMISSION    SYSTEM. 


141 


The  values  of  charging  current  in  Table  XIII  which  are  de- 
pendent upon  a  vohage  between  the  line  wires  and  the  neutral 
point  of  100,000  volts  for  a  single  mile  of  line  at  25  cycles  frequency 
and  a  given  spacing  are  obtained  by  substitution  in  the  formula 
(82). 

For   example,   assuming   the   conditions   of   the   transmission 

problem  above 

.0776 

0.0153  microfarad.  (St,) 

2log,o( 


C 


36 


102 


between  i  mile  of  No.  4  wire  and  neutral  with  36  in.  spacing 

2  -fCE 
1^  =  —---  (91) 


If 


10 

I^=  Charging  current  in  amperes  per  mile  at  100,000  volts 
f  =  Frequency  in  cycles  per  sec. 
C  =  Capacity  in  microfarads  per  mile. 
E  =  100,000  volts. 

2  TT  X  25  X  0.0153  ^  100,000 


I.= 


o.  239  amp. 


(91) 


10 

TABLE  XIII. 

Charging  Current  or  Single  Wire  in  Amperes  per  Mile  per  100,000 

Volts,  25  Cycles. 


' 

Spacing  in 

inches. 

Size  wire 

stranded. 

24 

36 

48 

60 

72 

84 

96 

108 

120 

ISO 

350000  cm. 

329 

.300 

.283 

.270 

.261 

•254 

.248 

•243 

•239 

•  230 

300000 

323 

■295 

.278 

.267 

.258 

•250 

•245 

.240 

•236 

.227 

250000 

316 

.290 

•274 

.262 

•253 

.246 

.241 

.236 

•  232 

.224 

Solid  4/0  B  &  S 

301 

.278 

.262 

■253 

•243 

•239 

•232 

.228 

.224 

.210 

3/0 

295 

.272 

•257 

•245 

■239 

•234 

.228 

.224 

.220 

.212 

2/0 

287 

.265 

.251 

.242 

■232 

.228 

.224 

.220 

.217 

.209 

0 

279 

.261 

.246 

■237 

.229 

.225 

.220 

.217 

.212 

.206 

I 

27s 

•251 

.242 

.229 

.223 

.220 

.217 

.212 

.209 

.203 

2 

268 

.250 

•237 

.226 

.221 

.217 

.212 

.209 

.206 

.199 

3 

264 

.246 

.229 

.225 

.217 

.2X2 

.209 

.206 

.203 

.196 

4 

25s 

■239 

.226 

.220 

.214 

.209 

.206 

•  203 

.200 

•193 

6 

245 

■  231 

.220 

.212 

.204 

.201 

.198 

•195 

.191 

.189 

14^ 


ELECTRIC    RAILWAY    ENGINEERING. 


This  value  will  be  found  in  Table  XIII  opposite  No.  4  wire  with 
36  in.  spacing. 

The  charging  current  for  any  other  voltage  (E')  between  wire 
and  neutral  and  for  any  other  length  of  line  (1)  is  of  course 


I\ 


or 


l'  = 


2  TziCE'l 
100,000  X  10* 


Table  value  x  1  x  E' 


100,000 


(92) 


(93) 


Again  considering  the  concrete  illustrative  problem  at  unity 
power  factor  the  charging  current  for  the  line  is 


^,      0.239x50x19,100 

I'  = =2.28  amp. 

100,000 


(93) 


It  will  be  seen  therefore  that  the  charging  current  with  this  par- 
ticular load  and  design  of  line  is  quite  an  appreciable  percentage 
(8.  7  per  cent.)  of  the  full  load  unity  power  factor  current.  The 
charging  current  might  be  decreased  somewhat  by  separating 
the  wires.  As  this  current  is  independent  of  load  its  percentage 
will  decrease  of  course  as  the  load  increases. 


l,.x, 


Fig.  56. — Vector  diagram  for  transmission  line  regulation  with  charging  current. 


In  refiguring  the  regulation  this  time  taking  the  charging 
current  into  account,  it  must  be  remembered  that  this  current 
leads  the  voltage  at  the  substation  (EJ  by  90  degrees.  The 
vector  diagram  of  voltages  is  therefore  represented  by  Fig.  56 
where  the  direction  of  the  charging  current  vector  and  therefore 
of  the  vector  of  resistance  drop  due  to  charging  current  (I^R)  is 
vertical  and  the  reactance  drop  due  to  charging  current    (I^XJ 


TRANSMISSION    SYSTEM.  143 

horizontal  since  (EJ  is  horizontal.  The  generator  voltage  (E"  ) 
may  be  seen  from  the  geometry  of  the  diagram  to  be 

E", = v/[e;+i7r~iX)h  (iwX,+ieR) '      (94) 

which  is  obviously  less  than  (Eg),  equation  (87),  since  the  charg- 
ing current  tends  to  neutralize  the  effect  of  line  inductive  re- 
actance, thereby  reducing  the  regulation  to  the  value 

Reg"=-^  (95) 

Substituting  the  numerical  data  of  the  above  problem 

E"g  =  V  (19,100+26.2  X  65.4  —  2.28  X  15.  5) ^  +  (26.  2  X  15.5  + 
2.28  X  65.4)^  =  20,760  volts  (94) 

20,760—  19,100 
Reg"=  -  =8. 7  per  cent.         (95) 

19,100 

A  similar  diagram  might  be  drawn  and  the  regulation  calcu- 
lated showing  the  effect  of  charging  current  with  low  initial 
lagging  power  factor  by  adding  the  triangle  of  charging  current 
fall  of  potential  to  the  diagram,  Fig.  55,  with  the  vector  (I  R) 
leading  (EJ  by  90  degrees. 

Comparing  the  regulation  found  by  taking  charging  current 
into  account  equation  (95),  with  that  which  neglected  that  partic- 
ular effect  equation  (88)  the  error  will  be  seen  to  be 

9-8.7 
Error  =    ^        =3.5  percent. 

which  may  safely  be  neglected  in  most  railway  work,  especially  as 
the  approximate  method  gives  the  highest  and  therefore  the  most 
conservative  estimate  of  the  regulation. 

It  is  believed  that  the  above  considerations,  together  with 
some  of  the  suggestions  regarding  high  tension  line  protection 
and  wiring  considered  in  Chapter  III  cover  the  more  important 
factors  involved  in  the  design  of  high  tension  lines  for  railway 
service.  For  further  details  of  construction  and  for  theoretical 
consideration  of  the  limiting  factors  which  enter  into  exception- 
ally high  voltage  installations  reference  should  be  made  to  the 
many  complete  works  on  these  subjects. 


144  ELECTRIC    RAILWAY   ENGINEERING. 

Estimates  of  construction  costs  on  both  distribution  and  trans- 
mission systems  have  been  purposely  omitted  owing  to  the  fact 
that  the  cost  of  copper  is  the  dominating  factor  in  these  portions 
of  the  railway  system  and  such  cost  is  so  variable  a  quantity  that 
estimates  or  costs  of  previous  installations  have  to  be  used  with 
great  caution  when  applying  them  to  proposed  systems. 


CHAPTER  V. 

Power  House  Location  and  Design. 

Whereas  the  complete  analysis  of  this  subject  would  require  a 
volume  of  generous  dimensions,  a  few  of  the  salient  features  to 
be  borne  in  mind  by  the  engineer  in  charge  of  the  planning  and 
construction  of  a  complete  electric  railway  system  may  well  be 
suggested. 

Location. — The  determination  of  the  proper  location  for  the 
power  house  from  the  one  standpoint  of  most  economical  trans- 
mission of  power  to  substations  is  made  in  a  manner  similar  to 
that  described  for  the  location  of  substations,  Chapter  III,  except 
that  in  this  case  the  various  loads  are  the  full  load  ratings  of  the 
various  substations  supplied  from  the  power  station  divided  by 
the  transmission  line  efficiency.  The  center  of  gravity  of  such 
loads  spaced  at  the  proper  distance  between  substations  locates 
the  power  station. 

With  the  power  station,  however,  many  other  factors  have 
to  be  considered  before  its  location  can  be  decided.  The  relative 
weight  of  these  factors  will  vary  with  local  conditions  but  they  are 
listed  below  in  the  order  of  importance  as  nearly  as  can  be  deter- 
mined for  the  average  case. 

The  question  of  cheap  coal  supply  to  the  steam  power  station 
is  all  important.  In  spite  of  this  fact  it  is  often  neglected  or 
given  little  thought,  especially  in  the  case  of  small  stations,  where 
it  is  often  believed  that  coal  may  be  drayed  to  the  station  at  rela- 
tively small  expense.  The  growth  of  traffic  and  competition  with 
steam  lines  unwilling  to  cooperate  with  respect  to  the  installation 
of  spur  tracks  or  track  connections  with  the  interurban  road,  have 
in  a  number  of  instances  seriously  embarrassed  small  interurban 
systems  or  at  least  prevented  the  power  station  reaching  a  reason- 
able cost  of  energy  output.  The  station  should  be  located  on  a 
railroad  siding,  or  better,  if  the  proposed  line  is  in  the  vicinity  of 
a  navigable  river,  many  of  the  other  factors  entering  into  the 
location  of  the  station  may  be  waived  in  order  to  locale  the  sta- 
lo  145 


146  ELECTRIC    IL'MLWAY    ENGINEERING. 

tion  at  a  point  where  the  coal  may  be  deposited  in  the  bunkers 
directly  from  the  coal  barges.  A  notable  example  of  such  loca- 
tion is  that  of  the  proposed  power  station  of  the  southern  in- 
terurban  line  previously  referred  to  which  is  distant  3  miles 
from  the  line  of  the  road  in  order  that  it  may  be  located  where 
ocean  going  coal  barges  may  be  docked. 

The  question  of  an  adequate  and  reasonably  soft  water  supply 
for  boiler  feed  and  condensing  purposes  should  receive  second 
consideration.  In  sections  of  the  country  where  it  is  necessary 
to  depend  upon  artesian  well  water  for  boiler  feed  it  is  either 
necessary  to  install  rather  expensive  water  softening  plants  or 
submit  to  a  high  maintenance  and  depreciation  charge  on  boilers 
with  considerable  risk  of  service  interruption.  The  marked  loss 
of  efficiency  and  corresponding  increase  in  cost  of  generated 
power  if  a  condensing  plant  is  occasionally  forced  to  operate  non- 
condensing  is  to  be  avoided  if  possible,  especially  in  the  case  of 
steam  turbines,  whose  principal  advantage  over  the  reciprocating 
engines  is  the  increased  economy  at  high  degrees  of  condenser 
vacuum.  Gravity  intakes  of  pipe  or  concrete  tunnel  construc- 
tion are  preferable  to  long  pipe  suction  lines  and  considerable 
expense  is  warranted  in  bringing  a  generous  supply  of  cold  pure 
water  into  the  cold  wells  of  power  stations  and  in  providing 
a  free  discharge  of  the  hot  well  to  waste  under  all  conditions  of 
water  level  in  flood  season  and  drought.  Especially  should  the 
purity  of  condensing  water  be  assured  with  the  surface  type  of 
condenser  used  to  such  an  extent  with  steam  turbines. 

Building  foundations,  especially  for  the  heavy  machinery  of 
the  station,  should  be  unquestioned  in  their  stability.  Many 
instances  may  be  quoted  in  which  the  saving  of  first  costs  of  test 
borings  or  real  estate  was  attempted  at  the  later  expense  of  the 
settling  of  foundations,  carrying  with  it  numberless  construction 
and  operating  difficulties.  Nor  is  it  sufficient  to  determine  the 
fact  that  there  is  good  subsoil  below  a  proposed  station  location. 
The  depth  of  excavation  necessary  to  reach  this  subsoil  and  the 
consequent  cost  of  foundations  should  be  carefully  learned  from 
preliminary  test  borings. 

The  power  station  often  acts  in  the  capacity  of  one  of  the  sub- 
stations on  the  line  supplying  the  high  tension  lines  to  other  sub- 


POWER    HOUSE    LOCATION    AND    DESIGN.  147 

Stations  not  only,  but  transforming  a  portion  of  the  generated 
electrical  energy  into  a  form  adaptable  to  the  nearby  trolley 
and  feeder  system.  This  plan  can  only  be  carried  out  when 
the  power  station  is  located  very  near  the  right  of  way  of  the 
railroad  as  the  low  voltage  of  the  distribution  system  is  not 
designed  for  transmission  to  any  considerable  distance. 

The  cost  of  real  estate  is  a  very  obvious  factor  in  the  determina- 
tion of  power  station  site.  With  an  interurban  road  the  center 
of  gravity  of  the  load  would  naturally  remove  the  station  from 
the  terminal  cities  where  the  cost  of  real  estate  is  probably  higher 
than  at  any  other  point  on  the  line,  but  the  operation  of  the  line 
or  a  portion  of  it  at  least  by  the  existing  power  companies  of  the 
terminal  cities  often  involves  power  station  additions  or  new 
locations  where  real  estate  is  high  in  cost.  This  sometimes  leads 
to  the  double-decking  of  stations  with  turbine  rooms  above  the 
boilers.  This  construction  has  the  further  advantage  of  short 
connections  between  boilers  and  turbines. 

A  feature  often  overlooked  in  the  selection  of  a  site  is  the  con- 
venience of  a  location  near  the  car  house  and  shops.  Such  a 
location  often  prevents  a  duplication  of  shop  equipment  and  the 
tools,  supplies,  and  even  labor  which  may  be  used  in  common, 
especially  in  case  of  emergency,  by  both  power  station  and  car 
shops  is  surprising.  Such  cooperation  between  the  departments 
of  a  large  railway  system  must  result  in  better  service  and  im- 
proved economy  of  operation. 

Closely  allied  with  the  above  is  the  necessity  of  locating  the 
station  at  a  point  where  employees  and  preferably  some,  if  not  all 
of  the  heads  of  departments,  are  willing  to  reside.  Especially 
in  the  emergencies  which  are  only  too  frequent  in  railway  opera- 
tion is  this  of  great  value  to  the  company. 

Within  the  city  limits  the  question  of  smoke  nuisance  sometimes 
has  a  bearing  upon  the  prol)lem,  but  as  expert  firing  and  special 
design  of  furnaces  with  the  possible  instal'ation  of  smoke  consum- 
ing devices,  if  efficient  ones  can  be  obtained,  reduce  this  trouble 
to  an  unobjectionable  minimum,  this  factor  has  little  weight  in 
placing  a  station. 

Design. -The  building  which  is  lo  house  the  generating  e(|ui]) 
ment  should  be  designzed  for  that  ]nirj)ose  primarily,  without  too 


148 


ELECTRIC    RAILWAY    ENGINEERING. 


much  thought  for  architectural  beauty.  Too  many  small  roads 
have  elaborate  stations  which  are  paying  little  or  no  returns  on 
the  investment  and  are  found  wanting  in  highly  efficient  equip- 
ment and  attendance.  Substantial  brick  or  concrete  buildings 
with  generous  basements  for  auxiliaries,  piping,  and  wiring  are 
necessary.  They  should  be  provided  with  plenty  of  head  room 
for  crane  operation  and  generously  lighted.  Such  a  power  sta- 
tion interior  is  illustrated  in  Fig.  57.  This  building  is  con- 
structed of  concrete  blocks  and  is  well  planned  to  house  the  single- 
phase  generating  equipment  of  the  Chicago,   Lake  Shore,  and 


Fig.  57. 


South  Bend  Railway,  at  Michigan  City,  Indiana.  This  photo- 
graph was  taken  at  night  by  means  of  the  mercury  vapor  lamps 
used  for  illumination. 

The  costs  of  power  station  buildings  cover  a  wide  range,  but  for 
a  fairly  large  modern  station  sufficiently  commodious  to  accom- 
date  all  necessary  machinery  without  overcrowding  a  figure  of 
from  $3.25  to  $3.50  per  square  foot  of  floor  area  should  be  allowed. 

The  question  of  vibration  and  foundation  construction  should 
be  given  very  careful  attention,  especially  where  high  speed 
reciprocating  machinery  is  employed.  Vibration  has  caused 
serious  difficulties  even  in  turbine  stations  of  the  double-decked 
type  with  the  turbines  located  on  the  second  floor.  Care  should 
be  taken  also  to  plan  for  future  extensions  in  the  construction  of 
the  buflding,  many  stations  being  carried  to  the  extreme  of  closing 


POWER   HOUSE    LOCATION   AND    DESIGN.  149 

one  end  with  temporary  corrugated  iron  construction  which  may 
be  readily  torn  down  as  extensions  are  made. 

Capacity. — In  determining  the  total  output  of  the  station, 
methods  similar  to  those  used  in  the  case  of  the  substation  are 
employed  with  due  consideration  being  given  to  the  "diversity 
factor."  This  factor,  which  has  only  recently  been  given  its 
proper  attention  by  operating  companies,  may  be  defined  as  the 
ratio  of  the  maximum  load  on  the  station  to  the  summation  of  the 
maximum  loads  of  the  various  substations.  That  is  to  say,  since 
the  maximum  loads  come  on  the  various  substations  at  different 
times,  the  capacity  of  the  power  station  may  be  considerably  less 
than  the  sum  of  the  substation  capacities.  The  only  accurate 
way,  therefore,  to  determine  the  probable  load  on  the  power  sta- 
tion is  to  plot  the  summation  of  all  the  substation  load  curves 
against  the  same  abscissae  of  time  and  divide  the  average  and 
maximum  values  of  this  load  curve  by  the  substation  and  trans- 
mission line  efficiency.  Such  a  load  curve  will  involve,  aside 
from  its  momentary  fluctuations,  two  or  more  well  defined  peaks 
which  must  be  taken  into  account  in  determining  the  number  of 
units  to  be  installed.  Reference  to  Chapter  III  will  recall  the 
method  of  subdividing  the  total  load  into  the  proper  number  of 
generating  units  which  is  equally  applicable  to  the  power  station, 
with  the  exception  that  extensive  subdivision  into  a  relatively 
large  number  of  small  units  involves  more  small  duplicate  auxil- 
iary equipment  in  the  case  of  the  power  station  incurring  corre- 
spondingly increased  maintenance  and  attendance  charges.  The 
generating  equipment  of  the  average  interurban  power  station 
will  not  include  more  than  three  units,  one  of  which  is  often  equal 
in  capacity  to  the  other  two  combined. 

Choice  of  Prime  Movers. — When  the  transmission  of  power 
from  a  nearby  water  privilege  with  its  relatively  low  cost  of  energy 
is  not  possible,  the  following  methods  of  driving  prime  movers  are 
usually  open  for  consideration  in  laying  out  a  new  power  station. 

1.  Reciprocating  steam  engines. 

2.  Steam  turbines. 

3.  Gas  engines. 

4.  \'arious  combinations  of  the  above. 

The  relative  advantages  of  the  various  prime  movers  and  their 


ISO 


ELECTRIC    R.AILWAY    ENGINEERING. 


combinations  arc  best  set  forth  by  cjuoting  Table  Xl\  published 
by  Mr.  H.  G.  Scott.  In  this  table  the  various  maintenance 
charges  of  each  type  of  installation  are  not  only  given  their  proper 
weights  but  the  variation  of  the  individual  charges  in  changing 
from  one  prime  mover  to  another  are  very  clearly  shown.  In 
addition,  the  relative  investments  necessary  for  the  various  types 
of  plant  are  compared  with  that  for  the  reciprocating  steam  engine 
plant  as  too  per  cent. 

T.\BLE  XIV.  1 
Distribution  of   MainteisI^nce  and   Operation   Charges   per   Kw.   Hour. 


Maintenance. 


Recip. 
engines. 


Steam 
turbines. 


Eng.  and 
turbines. 


Gas 
engines. 


Engine  room  mechanical .... 

Boiler  or  producer  room 

Coal  and  ash  handling,  appa 

ratus 
Electrical  apparatus 

Operation 
Coal  and  ash  handling  labor . 

Removal  of  ashes 

Dock  rental 

Boiler  room  labor 

Boiler  room  oil,  waste,  etc  .  .  . 

Coal 6 1 

Water 

Engine  room  mechanical  labor.  6 

Lubrication 

Waste,  etc 

Electrical  labor 

Relative  cost  of  maintenance        loo 

and  operation. 
Relative    investment    in    per        i  oo .  oo 

cent. 


Gas  en- 
gines and 
turbines. 


13 

I  . 

53 

0. 

74 

0 

79 

3 

17 

0 

31 

25 

57 

2 

71 

4 

■  77 

I 

■  30 

0 

■52 

2 

.67 

46 

1-54 
I-9S 


•  13 

•  53 
■74 
■03 

•  17 
.77 
•14 
•03 
.06 
■30 

•  52 

•  32 


Attention  should  be  called  to  the  fact  that  companies  that  have 
been  operating  railway  power  stations  with  reciprocating  engines 
are  realizing  the  marked  economy  which  can  be  obtained  by 
introducing  low  pressure  turbines  between  the  low  pressure 
cylinders  of  the  engines  and  condensers  and  many  such  combina- 
tion engine  and  turbine  stations  are  now  in  operation.  The 
output  of  a  condensing  engine  may  be  increased  from  20  to  25 
per  cent,  in  this  way  with  but  little  extra  space  occupied  and 
usually  without  building  additions.- 

'  Power  Plant  Economics  by  H.  G.  Scott,  A.  I.  E.  E.,  1906. 


POWER    HOUSE    LOCATION   AND    DESIGN. 


151 


152 


ELECTRIC    RAILWAY   ENGINEERING. 


The  status  of  low  pressure  turbine  development  may  perhaps 
be  best  judged  from  the  summary  of  the  report  of  the  Committee 
on  Power  Generation  of  the  American  Electric  Railway  Associa- 
tion in  1910  which  is  quoted  below  as  follows. 

"In  general,  the  installation  of  low  pressure  turbines  may  be 
recommended  wherever  there  are  good  engines  installed,  or  in 
the  case  of  a  new  installation  where  the  load  factor  and  the  coal 
cost  are  high.  In  plants  having  a  large  installation  of  a  good 
type  of  reciprocating  engine  the  low  pressure  turbine  may  be 
added  at  a  total  cost,  including  new  condenser,  auxiliaries, 
foundations,  piping,  etc.,  of  not  to  exceed  $25.00  per  kilowatt, 
thus  bringing  down  the  average  overall  investment  per  kilowatt 
of  the  entire  plant  and  so  reducing  the  fixed  charges  per  kilowatt- 
hour." 

In  deciding  whether  steam  turbines  or  engines  shall  be  installed 
the  question  of  steam  economy  naturally  receives  first  considera- 
tion. While  comparative  tests  under  exactly  similar  conditions 
have  probably  never  been  made  and  although  it  is  necessary  to 
make  some  assumptions  in  order  to  compare  fairly  the  test 
results  where  operating  conditions  vary  slightly,  the  following 
table  from  Kent's  Mechanical  Engineer's  Handbook  will  prob- 
ably compare  the  two  units  with  regard  to  economy  as  well  as 
any.  These  values  refer  to  a  600  h.  p.  horizontal  turbine  oper- 
ating with  saturated  steam  at  150  lb.  pressure  and  28  in.  vacuum 
and  an  850  h.  p.  compound  engine.  These  sizes  of  units  are  such 
as  are  often  found  in  interurban  power  stations. 

TABLE  XV. 

Comparative  Steam  Economy  of  Turbine  and  Compound 
Engine. 


Per  cent,  full  load. 

41 

75            100 

125 

Avg.  85 
per  cent. 

Pounds  water  per  brake  h.  p. 

600  h.  p.  turbine 

13.62 
13-78 

13-91 
13-44 

14.48 
13.66 

16.05 
17-36 

14-51 

850  h.  p.  compound  engine. .  .  . 

14.56 

POWER   HOUSE    LOCATION   AND    DESIGN.  1 53 

A  study  of  this  table  as  well  as  other  tests  under  nearly  identical 
conditions  indicates  that  there  is  little  choice  between  the  two 
units  from  the  standpoint  of  economy  alone. 

The  turbine  seems  to  be  the  unit  most  often  selected  at  the 
present  time,  however,  probably  because  of  its  advantages  over 
the  compound  engine  with  regard  to  first  cost,  space  occupied,  uni- 
form rotation,  freedom  from  vibration,  low  cost  of  foundations,  etc. 

Steam  Turbine. — If  the  steam  turbine  be  decided  upon  the 
following  items  should  be  given  particular  attention  in  writing 
the  specifications,  in  addition  to  the  usual  requirements  of  work- 
manship, grade  of  raw  material,  shipment,  etc.  \^alues  will  be 
substituted  for  a  particular  1500  kw.  specification  in  order  that 
the  requirements  may  be  of  more  value  for  reference. 

Rating,  1500  kw.  2300  volts,  3-phase,  60  cycles. 

Multistage,  ccmdensing. 

Steam  pressure,  150  lb. 

Back  pressure,  2"  referred  to  barometric  pressure  of  30" 

at  32°F. 

Superheat,  100°  F. 

Excitation,  125  volts. 

Full  load  temperature  rise  at  unity  power  factor,  rate^ 

voltage,  40°  C.  corrected  to  room  temperature  of  25°  C. 

Ch'erload  temperature  rise,    125   per   cent,    load,   rated 

voltage,  unity  power  factor  for  2  hr.'55°  C,  corrected  to 

room  temperature  of  25°  C. 

Momentary  overload  of  100  per  cent,  at  rated  voltage  and 

unity  power  factor  without  injury. 

Economy  expressed  in  lb.  steam  per  kilowatt  hour. 


Load  per 

cent. 

Economy, 

50 

20.  7 

75 

18.9 

100 

18.0 

150 

19.0 

Speed  regulation  at  end  of  heat  run,  speed  rise  when  unity 
power  factor  full  load  is  suddenly  thrown  off  shall  not 
exceed  4  per  cent,  of  normal  full  load  speed.     When 


154  ELECTRIC    RAILWAY    ENGINEERING. 

such  load  is  gradually  applied  the  speed  variation  shall 
not  exceed  2  per  cent,  of  normal  full  load  speed. 
Voltage  regulation  at  end  of  heat  run  when  load  is  thrown 
ofif  suddenly  shall  not  exceed  188  volts. 
Insulation  test  shall  be  applied  after  heat  run  of  5000 
volts  alternating  current  for  i  min.  between  armature 
coils  and  surrounding  conducting  material  and   1500 
volts  alternating  current  for  i  min.  between  field  wind- 
ing and  surroimding  conducting  material. 
A  non-condensing  run   shall   be  made  with  rated  load, 
power  factor,  voltage,  steam   pressure,  and  superheat 
against  atmospheric  pressure. 

Vibration. — The  units  shall  operate  smoothly  and  with- 
out undue  vibration  and  noise  under  all  conditions,  and 
all  revohing  parts  shall  be  accurately  balanced. 
Centrifugal  Stresses. — The  revolving  field  shall  be  sufifi- 
ciently  strong  to  resist  for  i  min.  without  injury  the 
centrifugal  stresses  produced  by  20  per  cent,  excess 
of  speed  with  armature  and  field  circuits  open. 

Steam  Engine. — The  features  of  particular  importance  in  the 
steam  engine  specifications  are  found  listed  below,  although  these 
specifications  do  not  refer  to  an  engine  for  railway  service. 

Type,  horizontal,  simple,  side  crank,  designed  to  run 

"over." 

Non-condensing. 

Rating,  375  h.  p.  at  most  economical  cut-off,  at  specified 

steam  pressure,  back  pressure,  and  normal  speed. 

Service, Aeii  hand  direct  connection  to   250  kw.   2200 

volt,  3-phase,  revolving  field  alternator. 

Speed,  200  r.  p.  m. 

Steam  pressure  to  be  125  lb.  dry  steam  at  throttle. 

Back  pressure  to  be  10  lb. 

Superheat,  none. 

Overload,  50  per  cent,  for  2   hr.,   momentary   overload 

of  100  per  cent,  without  injury. 

Economy  expressed  in  lb.  steam  per  indicated  h.  p.  hr. 

Speed  regulation  shall  not  exceed  i  1/2  per  cent,  of  nor- 


POWER    HOUSE    LOCATION    AND    DESIGN. 


mal  speed  when  full  load  is  suddenly  thrown  on  or  off. 
The  engine  shall  be  designed  to  operate  in  such  a  man- 
ner that  the  alternating  current  generator  to  which  it  is 


Fig.  59. 


connected  will  operate  successfully  in  parallel  with  other 
alternators  of  like  general  type. 
Generator.— The  consideration  of  the  relative  advantages  of 
engine  and  turbine  was  purposely  taken  up  first  in  order  that  the 


156  ELECTRIC   RAILWAY   ENGINEERING. 

necessity  of  installing  a  generator  might  be  determined.  If  the 
steam  engine  be  selected  the  alternating  current  direct  connected 
generator  will  find  a  place  in  the  power  station  equipment. 

It  is  of  course  necessary  to  know  the  generator  efficiency  in 
order  to  determine  the  brake  horse  power  rating  of  the  engine, 
the  latter  being  found  from  the  following  equation 


Gen.  output  in  kw  x  i.  34 
Eng.  brake  h.  p.  ^  ^^^^^ 


(96) 


It  is  not  only  unnecessary  but  inadvisable  to  specify  too  close 
regulation  for  alternators  in  railway  service.  That  the  regulation 
need  not  be  close  has  already  been  explained  in  connection  with 
the  transmission  line  design.  In  addition  to  that  fact,  however, 
it  will  be  remembered  that  if  close  regulation  be  not  required,  the 
reactance  and  armature  reaction  of  the  alternator  may  be  greater. 
This  tends  to  protect  the  rrachine  under  the  heavy  overloads  and 
short  circuits  to  which  it  is  likely  to  be  subjected  in  railway 
service  by  lowering  the  voltage  and  therefore  the  short  circuit 
current  of  the  armature.  The  latter  type  of  machines  also  has 
the  further  advantage  of  being  able  to  keep  in  synchronism  with 
one  another  more  readily  than  those  of  better  voltage  regulating 
qualities.  This  is  another  valuable  feature  in  railway  power 
station  operation. 

The  specifications  for  such  a  machine  are  materially  the  same 
as  for  the  generator  portion  of  the  turbine  previously  outlined, 
with  the  exception  that  the  speed  is  reduced  to  from  100  to  150 
r.  p.  m.,  and  in  some  installations  of  small  capacity  a  belted  ex- 
citer is  provided  for  each  generator. 

Transformers. — The  step-up  transformers  in  the  power  station 
are  identical  with  those  discussed  in  detail  in  Chapter  III,  the 
low  tension  winding  becoming  the  primary  in  this  case.  As  in 
the  case  of  the  substation  if  the  transmission  line  voltage  does  not 
exceed  13,000  volts,  the  generator  armatures  may  be  wound  for 
full  voltage  and  the  transformers  omitted. 

Transformer  specifications  should  include  the  rating,  frequency, 
primary  and  secondary  voltages,  type,  i.  e.,  whether  oil,  air,  or 
water  cooled,  temperature  rise  (50°  C.)  on  full  load,  provision  for 
50  per  cent,  overload  without  undue  heating  for  2  hr.,  efficiency, 


POWER   HOUSE    LOCATION   AND    DESIGN.  1 57 

power  factor  of  load,  insulation  test,  regulation,  etc.  Such  trans- 
formers as  would  be  used  in  power  station  service  might  be  ex- 
pected to  have  a  regulation  of  1.2  per  cent.,  a  full  load  efficiency 
of  98  per  cent,  or  slightly  more,  and  withstand  a  10,000  volt 
insulation  test  for  a  2200  volt  rating. 

Switchboard. — This  portion  of  the  power  station  equipment 
is  not  materially  different  from  that  described  in  connection  with 
substation  design  and  that  portion  which  may  be  installed  to 
control  substation  apparatus  in  the  power  station  is,  of  course, 
identical  therewith. 

Above  13,000  volts  and  often  below  that  voltage  the  board  is 
of  the  remote  control  type  with  switches  and  usually  cables  and 
transformers  as  well,  located  in  fire-proof  brick  or  concrete  cells. 
No  protective  device  is  installed  between  the  generators  and  the 
bus  bars,  although  the  out-going  transmission  lines  are  protected 
with  time  limit  relays,  lightning  arresters,  and  choke  coils.  For 
the  purpose  of  synchronizing  generators  and  in  order  to  balance 
the  loads  properly  between  the  various  machines  operating  in 
parallel,  the  generator  panels  are  often  equipped  with  auxiliary 
circuit  (125  volt)  control  devices  for  regulating  the  governors  and 
thereby  the  speed  of  the  prime  movers. 

Exciters. — Although  the  individual  alternators  are  occasion- 
ally provided  with  separate  belt-driven  exciters  especially  in  small 
installations,  it  is  customary  to  provide  a  steam-driven  and 
usually  a  motor-driven  exciter  set,  the  former  being  necessary 
in  starting  a  plant.  As  a  considerable  amount  of  125  volt  direct 
current  power  is  used  about  the  station  for  auxiliary  control  cir- 
cuits, etc.,  the  exciters  should  be  considerably  larger  than  the 
combined  demands  of  all  alternator  fields  which  they  are  called 
upon  to  supply.  In  selecting  the  e.xciter  capacity  it  should  also  be 
borne  in  mind  that  the  generators  at  low  power  factor  require  con- 
siderably increased  excitation  to  maintain  normal  voltage  at  full 
load  and  the  exciter  should,  therefore,  be  sufficiently  large  to 
supply  this  demand.  As  an  additional  protection  against  failure 
of  excitation  current  which  is  the  back  bone  of  the  power  plant, 
storage  batteries  are  often  "floated"  on  the  125  volt  bus  bars, 
ready  to  supply  energy  to  the  field  windings  in  case  of  failure  of 
the  exciters. 


158 


ELECTRIC    RAILWAY    ENGINEERING. 


SPTS  .xaonpojj 


POWKR    HOUSE    LOCATION    AND    DESIGN.  159 

Condensers. — As  most  railway  power  stations  are  operated 
condensing,  especially  when  turbines  are  installed,  the  various 
types  of  condensers  must  be  compared  and  a  selection  made  of  the 
most  suitable  for  the  purpose  at  hand.  Condensers  may  be  read- 
ily subdivided  into  three  classes. 

Jet  condensers  are  designed  to  spray  the  condensing  water  into 
the  steam  as  it  comes  from  the  low  pressure  cylinder  of  the  engine, 
the  steam  coming  in  direct  contact  with  the  water.  This  type 
is  extremely  simple  and  cheap  in  first  cost  but  in  cases  where  the 
condensing  water  is  unsuitable  for  boiler  feed  and  water  for  the 
latter  purpose  is  expensive,  the  jet  condenser  is  uneconomical  by 
reason  of  its  wasting  the  condensed  steam  which  might  otherwise 
be  used  again  in  the  boilers.  The  heat  in  the  exhaust  steam  is 
also  lost  in  this  case.  Pumps  are  provided  with  the  condenser 
for  supplying  water  and  extracting  air  and  water  from  the  con- 
densing chamber  and  thereby  maintaining  a  vacuum.  The 
former  pump  in  large  installations  is  usually  of  the  centrifugal 
type. 

Barometric  condensers  depend  upon  the  principle  that  atmos- 
pheric pressure  will  maintain  a  column  of  water  34  ft.  in  height 
in  the  tail  pipe  of  the  condenser  between  the  condenser  head  and 
the  hot  well.  This  necessitates  mounting  the  condenser  chamber 
34  ft.  above  the  hot  well  which  often  brings  this  chamber  above 
the  roof  of  the  power  house.  The  exhaust  steam  from  the  engine 
is  discharged  into  this  chamber  and  two  pumps  discharge  water 
into  and  extract  air  from  this  chamber  respectively.  The  vacuum 
is  maintained  by  the  syphon  action  of  the  column  of  water  while 
simply  the  air  which  is  entrained  in  the  condensing  water  is 
removed  by  the  air  pump  and  the  vacuum  thereby  improved. 
This  type  of  condenser  is  intermediate  between  the  other  two 
types  in  expense  but  is  usually  capable  of  maintaining  a  better 
vacuum  than  the  jet  type.  It  is  subject  to  the  same  disadvantages 
from  the  standpoint  of  feed  water  economy  as  the  jet  condenser. 

Surface  Condenser. — This  condenser  is  the  most  expensive  of 
the  three  types,  involving  as  it  does  a  series  of  tubes  mounted 
within  a  cast  iron  shell,  the  condensing  water  circulating  through 
the  tubes  and  the  steam  entering  and  being  condensed  in  the 
outside  shell.      As   the  condensed   steani   and  condensin*^  water 


l6o  ELECTRIC    RAILWAY   ENGINEERING. 

do  not  come  in  contact  with  one  another  the  former  may  be 
used  again  as  feed  water  and  its  initial  heat  used  to  advantage. 
Air  and  water  circulating  pumps  are  used  as  in  the  previous  types. 
Whereas  a  better  vacuum  can  be  obtained  with  a  surface  con- 
denser its  maintenance  and  tube  depreciation  are  high.  It  is 
not  in  extensive  use,  therefore,  except  with  steam  turbines  where 
the  slight  gain  in  vacuum  is  of  greatest  importance. 

The  amount  of  water  required  for  condensing  purposes  and 
therefore  the  si^e  of  condenser  and  piping  necessary  are  readily 
calculated  from  the  thermodynamic  equation 

H-h 

•   W  =  ^^  (97) 

where    W  =  Weight  of  condensing  water  in  pounds. 

H  =  Total  heat  in  steam  at  the  pressure  corresponding  to 
exhaust. 

h  =Heat  in  water  at  temperature  of  air  pump  discharge. 

T  =  Temperature  of  discharged  condensing  water  in  de- 
grees Fahrenheit. 

t    =  Temperature  of  the  entering  condesing  water. 

The  above  values  may  be  readily  obtained  from  the  steam 
tables  but  a  rough  approximation  of  (W)  may  be  made  by-as- 
suming average  values  of  the  above  units  as  follows: 

W=  1 1 50,  h=  120,  T=  no,  and  t=  70 
Whence 

1150—  120 

W  = =  25.8  lb.  water  necessary  to  condense  each  pound 

40 

of  steam. 

Total  water  necessary  per  h.  p.  hr.  is 

W}j  =  W  X  (Eng.  economy  in  pounds  steam  per  h.  p.  hr.)  (98) 
Multiplying  by  the  rated  indicated  h.  p.  of  the  engine  the  con- 
densing water  in  pounds  per  hour  is  determined. 

It  is  customary  to  use  a  factor  of  safety  above  this  figure  and 
while  30  lb.  of  water  per  h.p.  hour  is  a  figure  often  quoted, 
many  engineers  install  condensers  and  pumps  on  the  basis  of 
40  lb.  water  per  h.  p.  hour.  In  writing  specifications  for  con- 
densers it  is  the  usual  practice  to  refer  to  the  water  rate  of  the 
engine,  its  operating  pressures  and  the  probable  water  temper- 


POWER   HOUSE    LOCATION   AND    DESIGN. 


i6i 


l62  ELECTRIC    RAILWAY    ENGINEERING. 

atures,  and  require  the  manufacturers  to   furnish  a  condenser 
sufficiently  large  to  maintain  the  vacuum  most  economically. 

Boilers. — Knowing  the  amount  of  water  required  per  hour 
by  the  engines  or  turbines,  the  specified  water  rate  of  the  auxiliary 
pumps  may  be  added  directly  or  in  some  cases  the  assumption 
may  be  made  that  the  auxiliaries  will  take  from  2.5  to  5  per  cent, 
of  the  steam  taken  by  the  engines.  A  boiler  h.  p.  is  defined  as 
"the  evaporation  of  34.5  lb.  of  water  from  and  at  212°  F.  per 
hour."  The  boiler  rating  may  now  be  determined  from  the 
equation 

^   .,      ,  W(Xr+q-qJ 

Boiler  h.  p.  = (00) 

34-5 
where 

W  =  Steam  consumption  of  engines, and  auxiliaries  per  hour 

in  pounds. 
X    =  Percentage  of  (W)  which  is  dry  steam, 
r     =Heat  of  vaporization  of  steam  at  absolute  boiler  pressure 

from  steam  tables, 
q     =Heat  of  liquid  at  boiler  pressure  from  steam  tables, 
q^  =Heat   of  liquid  at   feed-water  temperature  from  steam 

tables. 
If  proper  consideration  has  been  given  to  the  overloads  de- 
manded at  different  times  of  day  and  during  the  various  seasons 
of  the  year  and  provision  made  for  a  sufficient  number  of  boilers 
being  constantly  out  of  service  to  guarantee  plenty  of  time  for 
cleaning,  the  capacity  of  the  boiler  plant  may  be  based  on  the 
above  equation,  the  size  of  the  units  being  the  next  standard  size 
above  that  given  by  the  above  equation.  The  largest  capacity 
installed  in  a  single  unit  is  500  h.  p. 

Boilers  are  broadly  classified  as  water-tube  and  fire-tube,  with 
a  large  number  of  varying  designs  under  each  classification.  In 
spite  of  the  fact  that  the  water-tube  boiler  is  the  most  expensive, 
it  is  rather  generally  installed  in  railway  plants  largely  because 
of  its  ability  to  steam  quickly  under  the  sudden  overloads  that  are 
experienced  in  railway  practice. 

Steam  boilers  require  a  special  foundation  with  ash  pits  opening 
below  the  boiler  room  floor,  usually  into  some  type  of  ash  con- 
veying machinery.     The  boiler  drums  and  tubes  are  freely  sup- 


POWER  housp:  location  and  design.  163 

ported  from  a  steel  frame  in  such  a  manner  that  they  may  readily 
expand  with  the  rise  in  temperature.  The  setting,  consisting  of 
fire  brick  arches  and  walls  surrounded  by  outside  walls  of  com- 
mon brick,  completes  the  installation. 

Boiler  specifications  should  cover  the  following  features: 

Rating  in  boiler  horse  power. 

Steam  pressure. 

Setting,  single  or  in  batteries. 

Type  of  support,  suspension  or  wall. 

Size  of  steam  and  blow-off  outlet  and  feed  water  inlet. 

Grate  area. 

Safety-valve,  gauges,  and  feed  check  valve. 

Weight  and  size  of  breeching  to  stack. 

Arrangement  of  arches. 

Hydrostatic  test. 

Mechanical  stokers  for  the  automatic  feeding  of  coal  from  the 
bunkers  to  the  furnaces  are  generally  installed  in  larger  plants. 
They  enable  one  fireman  to  care  for  several  more  boilers  than 
with  hand  firing  and  reduce  the  temperature  of  the  boiler  room 
considerably. 

Feed  Water  Heaters. — Reference  to  ecjuation  (99)  will  show 
that  if  the  initial  temperature  of  the  feed  water  entering  the 
boilers  (qo)  be  raised,  the  boiler  horse  power  required  for  a  given 
duty  will  be  less.  Add  to  this  the  lessened  strain  on  boiler  tubes 
and  plates  when  warm  water  is  fed  to  the  boiler  in  place  of  cold 
and  the  further  fact  that  this  rise  in  temperature  may  be  obtained 
by  the  use  of  heat  in  exhaust  steam  from  auxiliaries  or  from  the 
engine  itself  if  operating  non-condensing  and  the  economy  of 
installing  a  feed-water  heater  will  be  at  once  apparent.  Such 
devices  are  therefore  commonly  installed  in  the  boiler  room  and 
raise  the  temperature  of  the  feed  water  to  200  or  212°  F.  before 
it  enters  the  boiler.  The  feed-water  heater  may  be  either  the 
open  type  operating  at  atmospheric  pressure  or  the  closed  type 
in  which  the  water  is  forced  through  the  heater  by  the  feed  pump 
under  boiler  pressure.  Provision  is  made  in  the  heater  for  readily 
cleaning  from  same  the  scale  often  deposited  by  water  containing 
mineral  salts  and  in  many  installations  the  water-softening 
apparatus  of  the  hot-water  type  is  combined  with  the  heater  to 


164  ELECTRIC    RAILWAY   ENGINEERING. 

remove  the  scale  forming  chemicals  and  heat  the  water  in  one 
operation.  Specifications  need  inckide  only  the  boiler  horse  power 
supplied,  the  boiler  pressure,  the  average  normal  feed-water  tem- 
perature, and  the  approximate  amount  of  exhaust  steam  available 
for  heating  purposes.  If  the  apparatus  is  to  include  water- 
softening  equipment,  an  analysis  of  the  feed  water  or  a  sample  of 
same  must  accompany  the  specifications. 

Feed  Pumps. — Steam  driven  reciprocating  feed  pumps  of 
double  the  capacity  necessary  to  furnish  the  boiler  feed  water 
maximum  overload  should  be  installed  so  that  repairs  may  be 
made  at  any  time  without  crippling  the  service.  As  the  feed 
water  supply  is  the  back  bone  of  the  boiler  plant  its  design  should 
be  carefully  studied  and  generously  provided  for.  The  water 
should  flow  to  the  suction  of  the  feed  pumps  by  gravity  if  possible. 

Draft. — Although  mechanical  draft  of  the  forced  or  induced 
type  is  resorted  to  in  some  installations,  the  natural  draft  pro- 
duced by  chimneys  is  by  far  the  most  common.  A  single  stack 
is  usually  sufficient  for  a  medium  size  plant.  If  the  use  of  in- 
ferior grades  of  coal  is  contemplated  because  of  their  low  cost  the 
draft  provided  must  be  correspondingly  great.  As  the  draft 
produced  by  a  chimney  is  dependent  upon  its  height,  Mr.  J.  J. 
DeKinder  advises  that  the  following  heights  of  chimneys  be 
adopted  for  the  various  grades  of  coal. 

TABLE  XVI. 
Heights  of  Chimneys  for  Various  Grades  of  Coal. 


Coal. 

Height  in  feet. 

Free  burning  bituminous  coal 

75 
100 

Slow  burning  bituminous  slaclc 

Slow  burning  bituminous  coal 

115 

125 

150 

Anthracite  pea  coal 

Anthracite  buckwheat  coal 

As  the  formulae  used  in  chimney  design  involve  the  height  and 
area  and  as  the  capacity  in  boiler  horse  power  for  which  a 
chimney  can  supply  draft  is  proportional  to  the  latter  factor,  it 


POWER   HOUSE    LOCATION   AND    DESIGN.  1 65 

is  well  to  assume  the  height  iirst  for  the  degree  of  draft  required 
and  the  type  of  coal  used  and  calculate  the  necessary  area  of  cross 
section  from  formula  (loo).  Occasionally  the  reverse  process 
may  be  more  desirable. 

Kent's  formula  for  chimney  design  which  is  commonly  used  is 
Boiler  h.  p. 

3-33  vH 
where 

E  =  Effective  area  of  cross  section. 

H  =  Height  in  feet. 

Chimneys  of  small  dimensions  are  sometimes  constructed  of 
sheet  iron  but  in  larger  designs  are  either  common  brick,  Custodis 
radial  brick,  or  concrete.  Linings  are  provided  generally  for  one- 
half  or  the  entire  height  depending  upon  the  temperature  of  the 
flue  gases,  but  care  must  be  taken  to  have  the  lining  entirely  inde- 
pendent of  the  outside  walls  to  avoid  troubles  from  expansion 
and  contraction. 

That  the  cost  of  chimneys  is  an  item  of  some  consequence  in 
the  first  cost  of  the  power  plant,  especially  in  the  case  of  tall 
ornamental  chimneys,  will  be  noted  from  the  costs  and  estimates 
which  follow. 

Coal  and  Ash  Handling  Machinery. — The  judgment  of  the 
consulting  engineer  must  be  exercised  in  determining  the  extent 
to  which  coal  and  ashes  shall  be  handled  mechanically  in  a  plant 
of  given  size.  Where  mechanical  stokers  are  used,  some  type  of 
coal  and  ash  handling  machinery  is  generally  found,  usually  the 
continuous  belt,  bucket  type  of  apparatus  used  for  the  two  pur- 
poses of  removing  ashes  from  under  the  boilers  to  the  outside  of 
the  station  or  to  empty  cars  on  the  railway  siding  and  also  taking 
coal  from  the  crushers  and  delivering  it  to  the  overhead  bunkers. 
In  some  installations  ash  cars  running  longitudinally  under  the 
boiler  room  floor  convey  ashes  from  the  boilers  to  an  elevator 
shaft  and  thence  outside  the  building,  while  the  same  cars  and 
elevator  are  used  for  coal  hoisting.  This  is  cheaper  in  first  cost 
but  more  expensive  to  operate  than  the  former  type.  In  large 
stations  on  the  water  front  additional  efjuipment  is  found  for 
raising  coal  from  the  holds  of  coal  barges  to  the  crushing  machines. 
■  In  any  event  the  coal  and  ash  handling  machinery,  commonly 


1 66 


ELECTRIC    RAILWAY    ENGINEERING. 


electrically  operated,  is  expensive  in  first  cost.  It  reduces  the 
operating  charges,  however,  and  it  is  therefore  necessary  to  bal- 
ance the  fixed  charges  of  its  installation  against  the  saving  in 
operating  cost,  in  order  to  determine  whether  or  not  its  installa- 
tion is  warranted. 

Arrangement  of  Equipment. — The  most  convenient  arrange- 
ment of  apparatus  and  wiring  in  a  power  station  is  greatly  influ- 
enced by  local  conditions.     A  good  idea  of  such  arrangement  may 


Reinforced  Ciuder  Concrete 


Fig.  6: 


be  obtained  from  Fig.  58  which  represents  a  transverse  section 
through  the  boiler  and  engine  room  of  a  typical  power  station 
using  reciprocating  engines  direct  connected  to  alternators,  water- 
tube  boilers,  and  jet  condensers.  A  similar  section  through  the 
high  tension  switch  house  is  shown  in  Fig.  59.  A  plan  view 
of  a  gas  engine  station  will  be  found  in  Fig.  60,  while  Fig.  61 
shows  a  section  of  the  turbine  station  of  the  Indianapolis  and 
Cincinnati  Railway  Company  at  Rushvillc,  Indiana. 


POWER    HOUSK    LOCATION    AND    DESIGN. 


167 


Cost  of  Power  Station  Equipped. — Complete  power  stations 
including  buildings,  but  not  cost  of  land,  may  be  estimated  to  cost 
between  $100  and  Si 50  per  kilowatt  of  rated  output,  depending 
upon  the  elaborateness  of  design  and  the  addition  of  mechanical 
labor  savingand  safety  devices.  Occasionally  the  above  minimum 
figure  may  be  greatly  reduced,  as  was  the  case  of  the  rather  unic|ue 
double-decked  station  of  the  Fort  Wayne  and  Northern  Indiana 
Railway  Company,  Fig.  62,  located  in  Fort  Wayne,  Indiana, 
whose  detailed  costs  listed  in  Table  XVH  are  taken  from  a  paper 
before  the  American  Street  and  Interurban  Railway  Association 
by  Mr.  J.  R.  Bibbins. 

TABLE  XVH. 
Cost  of  Completed  Power  Station.    8500  Kw.     No  Stjbstation  Apparatus. 


Total  cost.       Cost  per  kw. 


Building:  Including  general  concrete  and  steel  work, 
galleries,  coal  bunker,  smoke  flue,  condenser  pit, 
coal-storage  pit,  etc. 

Generating  Plant:  Including  turbine,  generators,  ex- 
citers, cables,  switch-board,  transformers,  and 
ventilating  ducts. 

Boiler  Plant:  Including  boilers,  superheaters,  stokers, 
piping,  pumps,  heaters,  settings,  breechings,  and 
tank. 

Condenser  Plant:  Including  condensers,  pumps,  free 
exhaust,  water  tunnels,  and  intake  screen. 

Coal  Handling  Plant:  Including  gantry  crane,  crusher, 
motors,  and  track. 

Erection,  superintendence,  engineering,  and  miscel- 
laneous. 


S90' 


259.711 


118,: 


$10.97 


13 -92 


33.790 

3-98 

7>990 

0.94 

50,500 

5-94 

$563,520 

$66.25 

In  contrast  to  the  above  double-decked  station  there  may  be 
found  listed  below  the  final  estimate  exclusive  of  land  for  a 
modern  interurban  power  station  in  the  south  of  2000  kw. 
rated  capacity  involving  substation  equipment  of  300  kw. 
capacity.  This  estimate  is  given  in  considerable  detail  as  it  is 
believed  it  will  be  of  value  in  determining  the  relative  costs  of  the 


1 68 


ELECTRIC    RAILWAY   ENGINEERING. 


various  portions  of  the  equipment,  even  if  the  actual  prices  do 
vary,  as  they  must  from  time  to  time.  While  the  cost  has  been 
reduced  to  a  kilowatt  basis  it  should  be  stated  that  the  estimates 
are  from  detailed  figures  based  upon  actual  quotations,  the 
values  per  kilowatt  being  results  of  the  estimate  and  not  the  basis 
thereof. 


Estimate  for  Complete  Interurban  Power  Station  2000  K\v.  Rating  with 
300  Kw.  Substation  Equipment. 


Surveying  and  clearing  site 

Excavating  and  Grading  10,000  yd.  ©25  cents. 


Building  proper,  12,000  sq.  ft.  @  $3  .  25 

Machinery  foundations,    2   turbine  foundations,  100  yd. 

@  $10 

I  Stack  foundation,    200  yd.  @  $8 

2400  h.  p.  Boiler  foundation,  @  i  .60  h.  p 

2400  h.  p.  Boiler  settings  @  2 .  60  h.  p 

Miscellaneous  foundations,    100  yd.  @  10 


Stacks  and  Flues,  i  stack  g'xiSo'  (Custodis)  . 

2400  h.  p.  flues  @  1 .  00  h.  p 

Dampers,  Regulators,  etc 


Coal  and  ash  handling  apparatus,  loconaotive  crane. 

Conveyor,   crusher  and  scales 

Ash  cars  and  track 

Ash  pit 

Storage  yard  tracks,  etc 

Conveyor  trestle 


$300 
2500 


Cranes,  lighting,  plumbing,  etc.,  Crane. 

Lighting 

Plumbing 

Gratings,  railings,  etc 


Wells,  intakes,  etc 

Boilers,  stokers,  etc.,  boilers,  2400  h.  p.  &•  iS-So  erected. 
Stokers,  2400  h.  p.  (5   5  .  00  erected 


Piping,  valves,  etc 

Steam  turbines,  Curtiss  turbines  2-1000  kw. 
Frt.  and  starting 


Auxiliaries,  Heater,  1800  h.  p. 
Condensers,  2  @  $5,500.  . 
Feed  pumps,  2  @  1,100.  . 
Fire  pump,  i  @  1,100.  ..  . 

Oiling  system 

Freight  and  erection 


1000 
1600 
3850 
6250 
1000 

8000 
2400 


9000 
7500 
600 
500 
1500 
1000 

5000 
1500 
1000 
1000 


37200 
12000 


60000 
3000 

900 
1 1 000 
2200 
1 100 
1500 
2000 


Total 
cost 


8,500 

20,000 
49,200 
23,000 
63  000 


Cost  per 
kw. 


1.40 
1950 


6.8s 


10 .  00 
24  .60 
11.50 
31-50 


POWER    HOUSE    LOCATION   AND    DESIGN. 


169 


Estimate  for  Complete  Interurban  Power  Station  2000  K\v.  Rating  with 
300  Kw.  Substation  Equipment. — Continued. 


Total 
cost 


Cost  per 
kw. 


Generators,  exciters,  rotaries,  etc.,  Rotary  converter, 

300  kw.  @  $16.00 

Transformers,  480  kw.  @  10.00 

Turbine  exciters,  2-35  kw 

Motor-generator  set,  Ltg.  100  kw.  (fv  40.00 

Frt.  and  erection 


Switchboards  and  wiring,  16  panels. 

3  blank  panels 

Miscellaneous  brackets,  etc 

Frt.  and  erection 

Wiring  @  $1.50  per  kw 

Switch  cells 


Miscellaneous 

Sundry  supplies  and  expenses. 


Grand  total  exclusive  of  land  and  engineering  salaries 
and  commissions. 


4800 
4800 
3600 
4000 
2000 

7900 
ISO 
ISO 
1000 
3000 
1000 


2,500 
2.S00 


$304,300 


9.60 


6.60 


I  -25 
I.2S 


$IS200 


CHAPTER  VI. 
Bonds  and  Bonding. 

The  circuit  which  supplies  current  from  the  substation  to  the 
car  has  already  been  outlined.  The  return  portion  of  this  circuit 
is  made  up  of  the  track  rails,  being  augmented  by  return  copper 
feeders  in  parallel  with  the  track  only  incases  of  heaviest  service. 
As  rail  lengths  of  either  30  or  60  ft.  are  used  a  single  rail  will  have 
88  or  176  points  per  mile  at  which  the  electrical  resistance  of  the 
connection  between  rails  made  by  means  of  corroded  fish  plates 
would  normally  be  very  high.  With  this  high  resistance  directly 
in  series  with  the  return  circuit,  any  reasonable  addition  to  the 
copper  in  the  positive  feeders  is  of  little  value.  It  was  quickly 
found,  therefore,  in  the  operation  of  the  early  railway  systems 
that  the  ends  of  rails  must  be  connected  electrically  by  conductors 
of  lower  resistance  than  the  fish  plates.  These  conductors  have 
been  designated  as  "bonds." 

In  the  first  installations  bare  copper  negative  return  wires  were 
laid  along  the  ties  between  the  rails  and  connected  with  the  center 
of  each  length  of  rail  with  a  copper  wire.  This  method,  however, 
proved  very  expensive  and  was  abandoned,  although  it  has  been 
reinstated  recently  of  necessity  in  similar  form  where  traffic  is 
very  heavy,  particularly  in  city  systems.  Later  the  ends  of  rails 
were  bonded  by  means  of  No.  6  galvanized  wire  bonds  clamped 
under  the  heads  of  track  bolts.  Such  bonds  were  not  only  soon 
destroyed  by  galvanic  action  in  the  earth  but  were  found  to  be  of 
such  high  resistance  as  to  be  of  little  use.  A  slight  decrease  in 
the  contact  resistance  of  these  bonds  was  later  affected  by  forcing 
the  bond  wires  into  holes  drilled  in  the  heads  of  the  bolts.  The 
inability  to  reduce  the  track  resistance  sufficiently  by  any  of  the 
above  means  led  to  the  introduction  of  the  solid  copper  bond 
which  in  turn  developed  into  the  laminated  strip  copper  and 
stranded  copper  bonds  which  are  preferable  because  of  their 
flexibility. 

Several  distinctive  types  of  the  latter  bonds  have  now  come  into 

170 


BONDS    AND    BONDING.  171 

very  general  use  and  a  brief  description  of  each  will  therefore  be 
found  below. 

Compressed  Terminal  Bonds. — This  type  of  terminal  has 
been  applied  to  various  designs  of  copper  bonds.  It  consists  of  a 
cylindrical  head  varying  from  58  in.  to  i  in.  in  diameter  and 
slightly  longer  than  the  thickness  of  the  web  of  the  rail.  This  head 
is  forced  into  a  recently  reamed  hole  in  the  web  of  the  rail  by  means 
of  a  heavy  screw  clamp  provided  with  a  conical  contact  which 
engages  the  center  of  the  bond  head  and  causes  it  to  expand  and 
flow  under  the  pressure  applied  so  that  it  makes  intimate  contact 
with  the  inner  surface  of  the  hole  and  heads  over,  rivet  like,  so  as 
to  prevent  easy  loosening  or  removal.  Some  compressed  terminal 
bonds  have  their  heads  drilled  with  an  axial  hole  through  which  a 
tapered  steel  pin  in  driven  in  order  to  expand  the  copper  head 
well  into  the  hole  in  the  web. 

Compressed  terminal  bonds  may  be  installed  so  as  to  surround 
the  fish  plate  or  they  may  be  of  the  "protected"  type,  installed 
before  the  fish  plates  are  put  on  and  later  covered  by  the  latter 
plates,  thus  protecting  the  bond  from  mechanical  injury  or  theft. 
When  installing  this  bond  great  care  must  be  exercised  not  to 
drill  the  holes  much  before  the  bonds  are  inserted  and  to  use  a 
lubricant  when  drilling  holes  which  will  not  produce  an  insulating 
film  on  the  inside  surface  of  the  hole.  Clear  water  or  a  solution 
of  bicarbonate  of  soda  and  water  may  be  used  but  oil  and  soapy 
water  should  not  be  tolerated  as  lubricants. 

Soldered  or  Brazed  Bonds. — Bonds  similar  to  the  above  but 
with  flat  tinned  heads  are  sometimes  soldered  or  brazed  to  the 
side  of  the  rail  head  or  under  the  rail  flange  by  means  of  a  gasoline 
or  oxy-hydrogen  blow-torch  after  the  rail  has  been  brightened  at 
the  point  of  contact.  These  bonds  have  not  proved  entirely 
satisfactory,  however,  as  they  are  cjuite  likely  to  work  loose  and 
are  also  quite  easily  stolen. 

Electrically  Welded  Bonds. — A  process  of  electrically  welding 
a  short  laminated  copper  bond,  provided  with  a  brass  head,  upon 
the  sides  of  the  rail  heads  has  recently  been  developed.  This  is 
accomplished  by  the  use  of  a  very  large  alternating  current  passing 
through  the  very  small  areas  of  bond,  rail  head,  and  carbon  ter- 
minal in  series  and  thus  bringing  the  two  metals  to  a  welding  heat. 


172 


ELECTRIC    RAILWAY    ENGINEERING. 


While  this  process  is  termed  welding  it  is  more  correctly  brazing, 
since  two  different  metals  are  joined  with  a  flux  of  borax  between. 
The  large  alternating  current  necessary  is  produced  by  making 
the  yoke  and  jaws  which  grip  the  bond  and  rail  head  a  part  of  the 
secondary  circuit  of  a  current  transformer  whose  primary  is 
supplied  from  the  alternating  current  side  of  an  inverted  syn- 
chronous converter.  This  converter  is  mounted  on  the  car  which 
carries  the  bonding  outfit  and  is  supplied  with   direct  current 


Fig.  65 


from  the  trolley.  The  ratio  of  transformation  and  impednace  of 
the  transformer  secondary  circuit  are  such  that  the  current  flowing 
through  the  weld  is  in  the  neighborhood  of  1000  amperes.  The 
particular  equipment  from  which  these  values  were  obtained, 
Fig.  63,  involves  a  15  kw.  transformer  supplied  from  and  18  kw. 
inverted  synchronous  converter  operating  at  a  frequency  of 
25  cycles.  The  transformer  was  connected  for  two  voltages  of 
375  and  500  volts  respectively,  while  the  secondary  voltage  varied 
from  one  to  seven  volts.  The  converter  was  also  used  as  a  motor 
to  propel  the  car. 


BONDS   AND    BONDING.  1 73 

In  this  particular  test^  with  the  500  volt  connection,  the  time 
required  to  make  a  weld  averaged  82  sec.  with  an  input  to  the 
car  per  bond  of  797  watt  hours.  An  estimate  of  the  cost  of 
electric  welding,  assuming  that  40  welds  per  day  can  be  made 
would,  therefore,  result  as  follows,  if  power  costs  2.5  cents  per 
kilowatt  hour  at  the  car. 

Cost  of  energy  0.797X.025 $.019 

Cost  of  bond 30 

Cost  of  labor 112 

Sundries 01 


$.441 


This  estimate  is  slightly  low  since  it  is  always  necessary  to  grind 
a  bright  place  on  the  head  of  the  rail  before  the  bond  is  applied. 
This  is  accomplished  by  means  of  an  electric  motor-driven  grinder 
connected  with  the  trolley.  The  power  for  this  purpose  was  not 
included  in  the  above  estimate,  although  a  labor  item  was  allowed 
to  cover  the  work.  It  is  safe  to  say,  however,  that  these  bonds 
may  be  installed  for  45  cents  each  while  the  other  types  vary  from 
something  less  than  this  up  to  70  cents,  each  installed. 

Amalgam  Bonds. — Bonds  consisting  of  semiplastic  amalgam 
forced  between  the  brightened  surfaces  of  rail  web  and  fish  plate 
are  occasionally  found,  although  not  in  common  use. 

Aside  from  the  above,  several  methods  of  making  continuous 
rail  joints  of  high  electrical  conductivity  may  wtU  be  classified 
under  the  heading  of  bonds.  Such  methods  in  common  use  are  as 
follows : 

Cast  Welded  Joint. — In  making  this  joint,  melted  iron  of 
special  composition  and  high  conductivity  is  poured  around  the 
rail  ends,  with  the  exception  of  the  heads,  while  they  are  enclosed 
in  a  sand  or  iron  mould  of  such  shape  as  to  leave  a  heavy  lug  of 
cast  iron  about  the  ends  of  the  rail.  While  it  is  rather  difficult 
with  this  process  to  raise  the  temperature  of  the  rail  quickly 
enough  to  insure  molecular  adhesion  between  the  rail  and  the 
molten  metal,  yet  very  satisfactory  results  have  been  obtained  in 
many  instances  from  both  the  standpoints  of  electrical  conduc- 
tivity and  mechanical  rigidity. 

'  Thesis,  Purdue  University,  1910,  by  Broadwell,  Cole,  and  Stevenson. 


174  ELECTRIC    RAILWAY    ENGINEERING. 

Thermit  Welded  Joint. — A  combined  joint  and  bond  of  com- 
paratively recent  origin  is  produced  by  the  "  thermit"  process.  As 
in  the  previous  method  a  mould  of  sand  is  made  about  the  rail 
ends  but  in  this  case  only  sufficient  thermit  for  one  joint  is  melted 
at  a  time.  This  melting  is  accomplished  by  making  use  of  the 
well  known  fact  that  finely  divided  aluminum  when  oxydized 
develops  a  great  amount  of  heat.  This  reaction  has  been  recently 
brought  under  control  so  that  a  small  amount  of  powdered  alumi- 
num mixed  with  iron  oxide,  if  ignited  with  a  small  amount  of 
ignition  mixture,  will  react  as  above  explained  with  sufficient  heat 
to  melt  the  iron  which  in  turn  is  poured  about  the  rail  ends.  This 
produces  a  joint  similar  to  the  cast  weld  with  less  metal  but  with 
apparently  quite  as  good  electrical  and  mechanical  characteristics. 

Electric  Welded  Joint. — In  contrast  to  the  electric  welded 
bond  mentioned  above  there  may  be  found  in  the  city  tracks  of 
many  railway  companies  the  electric  welded  rail  joint.  This,  a 
rigid  rail  joint,  produced  by  electrically  welding  heavy  iron  bars 
on  either  side  of  the  webs  of  adjacent  rail  ends,  should  be  carefully 
differentiated  from  the  electric  welded  bond,  although  the  proc- 
ess of  welding  is  almost  identical  with  that  outlined  above,  with 
the  exception  that  iron  only  is  used  and  the  si2,e  of  weld  and  corre- 
sponding power  used  are  much  greater.  In  this  latter  type  of 
joint  iron  filler  blocks  are  inserted  between  the  rail  ends  and 
ground  to  the  form  of  the  rail  head  so  that  the  joint  is  entirely 
closed  and  the  operation  of  cars  over  rail  joints  is  made  so  much 
the  smoother.  This  joint  has  given  very  satisfactory  service  both 
electrically  as  a  bond,  for  its  conductivity  is  practically  equal  to 
that  of  the  rail,  and  mechanically  as  a  rail  joint,  the  breakages 
not  exceeding  i  per  cent,  of  the  total  joints  welded  after  several 
years  of  service  in  at  least  one  installation  and  averaging  very 
close  to  this  record  on  several  other  roads. 

When  considering  any  of  these  three  methods  of  making  combi- 
nation rail  joints  and  bonds  where  the  joint  is  necessarily  mechan- 
ically rigid,  it  should  be  borne  in  mind  that  the  track  will  expand 
in  hot  weather  sufficiently  to  throw  it  noticeably  out  of  gauge 
if  it  is  not  rigidly  held  in  place  by  street  paving.  None  of  these 
methods  are  therefore  suitable  for  anything  but  i)aved  city  streets, 
unless  an  exception  be  made  of  the  few  cases  where  they  ha\'e 


BONDS   AND    BONDING. 


175 


been  tried  with  expansion  joints  every  few  hundred  feet.  At 
these  joints  of  course  some  other  type  of  bond  must  necessarily  be 
installed. 

As  these  processes  combine  a  rail  joint  with  a  bond,  doing  away 
with  fish  plates,  track  bolts,  and  other  types  of  bonds,  their  expense 
is  naturally  much  greater  than  that  of  any  other  bond  alone. 
^Herrick  and  Boynton  give  average  prices  for  these  combined 


Vi)ltiueter 


Ac.  Side  Kotai-y 


Ammeter 


Dc.  Side  Rotary 


Voltmeter 


Special  Current 
Trausl'ormer 


^  Couuected  to  Bond  Clamps 
Fig.  64. — Connections  for  electric  welding  of  honds. 

joints  of  from  $2.67  each  for  cast  welded  joints  and  $4.50  each  for 
the  "Thermit"  process,  up  to  %S-5'^  o^  $6.00  per  joint  for  the 
electric  weld.  These  figures  do  not  include  opening  and  closing 
the  pavement  around  the  joint  in  case  old  track  is  being  treated, 
which  cost  will  vary  from  Si. 00  to  $1.25  per  joint. 

Bond  Testing.  The  bond  resistance  of  a  well  bonded  track 
using  4/0  B  &  S  bonds  will  range  from  5  to  7  per  cent,  of  the 
resistance  of  the  track  return.  With  a  few  missing  bonds  or 
with  poor  contacts  between  bonds  and  rails  this  resistance  may 


.American  Electric  Railway  Practic  e,  hv  Ilerrick  and  Bovnton. 


176  ELECTRIC    RAILWAY   ENGINEERING. 

be  increased  many  times.  While  the  maximum  allowable 
voltage  drop  in  the  return  circuit  is  often  very  rigidly  fixed  in  the 
city  systems  by  municipal  ordinance,  it  is  for  the  interest  of  the 
operating  company  to  keep  this  resistance  at  a  minmium  value, 
since  the  voltage  at  the  car  varies  inversely  and  the  losses  vary 
directly  w^ith  the  resistance.  It  has  been  customary,  therefore,  to 
make  frequent  tests  of  the  resistance  of  rail  bonds  and  the  stand- 
ard has  been  rather  arbitrarily  set  that  the  resistance  of  a  bond 
shall  be  less  than  that  of  3  ft.  of  rail. 

The  comparison  of  the  resistance  of  the  bond  with  that  of  3  ft. 
rail  may  be  very  readily  made  by  making  use  of  the  current 


o        o     ll     o        o 


Fig.  65. — Connections  of  bond  testing  meters. 

flowing  in  the  rail.     Two  contacts,  (a)  and  (b)  Fig.  65,  consisting 

of  hardened  steel  knife  edges  or  points  connected  to  a  milli- 

voltmeter  (V)  are  applied  to  the  head  of  the  rail  at  a  distance  apart 

corresponding  to  the  length  of  the  bond.     A  third  contact  (c)  is 

permanently  spaced  3  ft.  distant  from  one  of  the  former  contacts, 

(b).     If  another  milli- voltmeter  (V)  be  connected  between  (b) 

and  (c)  and  read  simultaneously  with  the  meter  connected  to  (a) 

and  (b)  the  readings  are  proportional  to  the  resistance  of  a  3-ft. 

section  of  rail  and  that  of  the  bond  respectively.     The  bond  may 

be  pronounced  in  satisfactory  condition  if 

V<V'  (loi) 

while  if  (V)  be  too  great  its  departure  from  the  required  value 

may  be  recorded  as 

ioo(V-VO 

percent.  (102) 

Care  must  be  exercised  in  making  these  tests  not  to  damage 
the  milli-voltmeter  by  attempting  to  measure  an  open  bond. 
It  is  always  well  to  try  the  bond  on  a  meter  with  a  15  volt  scale 
first  and  if  the  drop  in  potential  is  found  to  be  within  the  range 


BONDS   AND    BONDING.  '  1 77 

of  the  milli-voltmeter  to.  make  the  final  reading  with  the  latter 
instrument. 

As  this  process  is  a  rather  slow  and  tedious  one  where  there 
are  a  large  number  of  bonds  to  be  tested,  various  methods  have 
been  devised  for  making  the  tests  on  a  car  as  the  latter  is  traveling 
over  the  road.  Usually  this  is  necessarily  done  when  the  regular 
cars  are  off  the  line  at  night  or  with  very  little  varying  current  in 
the  rails.  The  current  sufficient  to  determine  the  voltage  drop 
in  rail  sections  and  bonds  is  fed  through  the  local  rail  section  by 
means  of  specially  designed  trucks,  the  current  being  controlled 
by  a  rheostat  on  the  test  car.  ^ 

If  it  be  desired  to  learn  only  the  total  resistance  of  the  track 
return  this  may  be  determined  after  the  cars  are  off  a  section  of 
line  by  passing  a  measured  current  through  the  rails  by  means  of 
a  feeder  to  the  distant  end  of  the  line  and  a  rheostat  at  that  point 
in  series  therewith.  A  second  feeder  may  be  disconnected  from 
the  generator  temporarily  and  used  as  a  potential  lead  so  that  the 
fall  in  potential  in  the  track  may  be  read  upon  a  voltmeter  in  the 
power  house. 

Cross  Bonding. — Thus  far  the  bonding  of  rail  ends  alone  has 
been  considered.  It  is  sometimes  necessary  to  provide  against 
the  greatly  increased  resistance  of  the  return  circuit  due-  to  a 
possible  open  bond  by  connecting  the  rails  together  electrically 
by  means  of  cross  bonds  spaced  several  hundred  feet  apart. 
These  usually  consist  of  bare  copper  wire  of  approximately  the 
size  of  the  bonds  soldered  to  the  bonds  on  opposite  rails  or  to 
special  single  headed  bond  terminals  forced  into  the  rail  web. 
Thus  if  a  bond  be  open,  the  return  current  on  that  particular 
rail  would  follow  the  nearest  cross  bond  to  the  other  rail  and  find 
its  way  back  to  the  original  rail  at  the  next  cross  bond  nearest  the 
power  station. 

As  the  bonding  of  all  joints  in  special  track  work  such  as 
switches,  cross-overs,  and  frogs  would  often  involve  a  large  numljer 
of  bonds,  a  heavy  cable  is  often  laid  around  such  portions  of  the 
track  and  thoroughly  bonded  to  the  sections  of  track  on  either 
side  thereof. 

'  Practical  P21ectric  Railway  Handbook  bv  Herrick. 


CHAPTER  VII. 

Electrolysis. 

The  subject  of  the  electrolysis  of  underground  pipe  systems  is 
so  closely  allied  to  that  of  bonding  that  no  sharply  defined  line 
can  be  drawn  between  them.  Beginning  with  the  rather  general 
introduction  of  the  direct  current  street  railway  systems  in  the 
early  nineties,  with  their  track  return  and  relatively  poor  bond- 
ing, and  extending  through  the  rapid  development  and  improve- 
ment of  such  systems,  the  question  of  electrolysis,  its  cause  and 
prevention,  has  maintained  an  important  although  ever  decreas- 
ing prominence  in  the  studies  and  discussions  of  the  engineers  of 
gas  and  water  works  corporations  as  well  as  the  telephone  and 
street  railway  interests. 

It  has,  of  course,  been  known  for  a  long  time  that  if  a  direct 
current  be  allowed  to  flow  from  a  metal  electrode,  through  an 
electrolyte  to  a  second  metal  electrode,  a  chemical  reaction  takes 
place  at  the  expense  of  the  positive  plate,  i.e.,  this  plate  is  actually 
eaten  away,  the  metal  removed  therefrom  forming  a  salt  with 
some  of  the  acid  radicals  of  the  electrolyte.  During  these  reac- 
tions which  take  place  similarly  when  moist  earth  is  the  electro- 
lyte it  was  noticed  that  hydrogen  was  given  off  at  the  cathode  or 
negative  terminal  while  oxygen  was  liberated  at  the  anode.  It 
was  supposed  for  some  time  that  those  free  gases  were  formed 
from  the  decomposition  of  the  water  in  the  earth.  When  it  was 
later  found,  however,  that  this  action  often  took  place  with  poten- 
tials between  terminals  of  the  order  of  hundredths  and  even 
thousandths  of  a  volt,  which  are  not  suft'icient  to  decompose  water 
and  free  these  gases  at  their  respective  electrodes,  a  further  study  of 
the  problem  was  undertaken. 

Experiments  carried  on  at  the  University  of  Wisconsin  and 
recorded  in  the  discussion  of  a  very  able  paper  upon  this  subject 
presented  before  the  American  Institute  of  Electrical  Engineers 
by  the  late  Isaiah  H.  Farnham  in  1894  demonstrated  the  fact  that 

178 


ELECTROLYSIS.  179 

with  iron  electrodes  embedded  in  moist  earth  electrochemical 
action  is  substantially  as  follows:  Most  earths  contain  salts  of 
alkaline  metals.  Merely  a  directive  electromotive  force  of  the 
order  of  .001  volt  will  cause  the  acid  radical  of  these  salts  to  be 
isolated.  This  radical  then  attacks  the  anode.  Suppose  sodium 
sulphate  (NaSOJ  be  present  in  the  earth;  this  is  broken  up  by 
the  current  into  (Na)  and  (SO J.  The  SO^  forms  with  the  posi- 
tive iron  electrode  (FeSO  J  while  the  hydroxide  of  sodium(NaOH) 
is  formed  at  the  cathode.  When  the  earth  in  the  neighborhood  of 
the  terminals  becomes  saturated  with  these  compounds  they  dif- 
fuse toward  one  another  and  finally  meet  in  the  earth  at  a  point 
easily  detected  by  the  formation  of  a  green  precipitate  of  ferrous 
hydroxide  and  the  original  salt.  This  reaction  causes  a  local  rise 
in  temperature  at  the  point  where  the  precipitate  forms.  The 
reactions  mentioned  above,  which  take  place  at  the  electrodes, 
release  oxygen  gas  at  the  anode  and  hydrogen  at  the  cathode,  the 
former  resulting  from  an  excess  of  SO^  forming  an  acid  with  the 
hydrogen  of  the  water  and  setting  oxygen  free.  The  latter  is  the 
result  of  the  formation  of  the  hydroxide  of  sodium  with  water; 
the  free  atom  of  hydrogen  from  the  water  being  liberated. 

The  one  point  of  i)ractical  interest  in  this  series  of  reactions  is 
the  fact  that  iron  is  removed  from  the  positive  electrode  to  make 
ferrous  sulphate  and  later  ferrous  hydroxide,  and  the  size  and 
weight  of  this  plate  are  reduced  thereby.  This  loss  of  metal 
from  the  buried  plate  is  proportional  to  the  current  flowing  there- 
from. Now  if  the  track  return  circuit  be  of  high  resistance,  a 
])ortion  of  the  return  current  will  flow  back  to  the  power  station  on 
underground  pipes  and  cable  sheaths,  leaN'ing  these  conductors  at 
points  near  the  power  station  to  complete  the  circuit  through  the 
earth  or  on  the  rails  and  negative  cables  to  the  switchboard. 

Since  the  above  chemical  reactions  take  place  in  the  case  of 
electric  railway  currents  leaving  water  and  gas  mains  and  the 
sheaths  of  telephone  cables  and  entering  the  earth  with  values 
ranging  from  an  infinitesimal  leakage  uj)  to  se\'eral  hundred 
amperes  in  extreme  cases,  the  importance  of  the  study  of  the  mag- 
nitude of  troubles  from  electrolysis  and  the  remedies  to  l^e  ap])lied 
is  at  once  apparent. 

Jn  the  early  days  of  electric  traction  the  bonding  of  the  track 


i8o 


ELECTRIC    RAILWAY    ENGINEERING. 


and  the  proper  installation  of  a  low-resistance  return  circuit  were 
seriously  neglected  as  has  been  explained  in  the  previous  chapter. 
It  was  also  customary  at  first  to  connect  the  negative  terminal 
of  the  generator  with  the  trolley  and  the  positive  to  the  rail  in 


Pipe  or  Lead  Cable 
Fig.  66. — Direction  of  current  with  negative  trolley. 


P'IG.    67. 

many  installations,  this  being  just  the  reverse  of  the  present 
method.  These  two  conditions  tended,  first,  to  force  a  relatively 
large  proportion  of  the  current  to  follow  the  pipe  and  cable  sys- 
tems in  place  of  the  track  and,  secondly,  to  make  such  pipe  and 
cable  systems  positive  to  the  rail  over  a  wide  area  of  territory  in 
the  average  city. 


ELECTROLYSIS. 


I»I 


This  condition  is  clearly  shown  in  the  accompanying  Fig.  66, 
which  shows  the  direction  of  earth  currents,  and  Fig.  67,  represent- 
ing the  conditions  in  Boston,  Mass.  when  the  question  of  danger 
from  electrolysis  was  first  seriously  considered.  At  the  time  this 
map  was  plotted  from  a  large  number  of  tests  made  of  the  voltage 
between  pipe  systems  and  rails,  the  trolley  was  negative  and  the 
rails  positive.  The  shaded  area  designated  as  the  " danger  area" 
represents  the  territory  in  which  the  pipe  systems  are  positive 
to  the  rails  and  therefore  in  which  electrolysis  might  be  expected 
to  take  place.  The  large  extent  of  this  danger  area  implies  a 
great  amount  of  possible  trouble  from  electrolysis  and  a  consid- 
erable expenditure  of  time  and  money  for  the  proper  maintenance 
of  tests  and  the  location  of  serious  leakages  of  current. 


+ 


^ 


Bl^^  ^^ 


Pipe  01  Lead  Cable 
Fig.  68. — DirectiDii  of  current  with  positive  trolley. 


A  marked  advance  was  soon  made,  however,  in  this  problem 
when  the  trolley  was  connected  with  the  positive  terminal  of  the 
generator  and  the  rails  with  the  negative  terminal  as  in  Fig.  68. 
This  change  would  naturally  limit  the  danger  zone  to  a  compara- 
tively small  area  near  the  power  station  where  the  current  which 
returned  on  the  various  pipe  lines  would  leave  these  conductors 
and  pass  through  the  earth  to  the  rails  or  return  conductors  and 
thence  to  the  negative  terminal  of  the  generator.  The  effect  of 
such  a  reversal  of  trolley  polarity  is  obvious  in  Fig.  69  which 
represents  a  potential  map  of  the  territory  included  in  Fig.  67 
taken  after  the  trolley  of  the  West  End  system  of  Bostpn  was 
made  positive.     This  limitation  of  the  area  in  which  electrolysis 


I«2 


ELECTRIC    RAILWAY    ENGINEERING. 


may  take  place  would  usually  increase  the  current  leaving  the 
pipes  at  any  one  place.  To  prevent  serious  trouble  from  elec- 
trolysis at  those  ])oints  it  is  customary  to  connect  the  pipes  with 
the  rails  or  return  negative  feeders  by  means  of  heavy  copper 
cables.  In  fact  this  practice  is  often  employed  at  other  points 
along  the  line  where  pipes  are  found  to  be  positive  to  the  rail. 
This,  policy,  however,  unless  carefully  carried  out,  often  in- 
cr  eases  the  electrolytic  effects  from  any  pipes  which  happen  to 


EAST 
Iff        BOSTON 


Fig.  6o. 


be  left  unconnected  with  the  rails  because  of  the  greater  area 
exposed  by  negatively  connected  pipes  and  therefore  the  presence 
of  lower  resistance  paths  through  the  earth.  Such  a  condition 
is  well  illustrated  by  Fig.  70. 

In  this  connection  it  might  be  of  interest  to  note  some  of  the 
results  of  electrolysis  with  currents  of  different  magnitudes. 
Experiments  have  proved  that  one  ampere  flowing  steadily  from 
an  iron  surface  will  remove  approximately  20  lb.  of  iron  in  one 
year,  while  the  same  current  flowing  continuously  from  a  lead 
cable  sheath  or  pipe  will  eat  away  75  lbs.  of  lead  in  the  same  time. 
A  48  in.  iron  water  main  in  Boston  was  pitted  in  various  places 
to  a  depth  of  9/16  in.  in  from  four  to  five  years,  the  average  po- 
tential  between    pipe   and   rails   being   8    volts   wdth  a  current 


ELECTROLYSIS. 


183 


flowing  in  the  pipe  ranging  from  5  to  95  amperes.  In  this  case 
the  pipe  was  about  21/2  ft.  below  the  rails  of  the  street  railway 
company. 

Nor  is  the  trouble  conhned  alone  to  the  points  where  the 
current  leaves  the  pipe  for  other  conductors.  The  joints  in  pipe 
lines  often  have  relatively  high  resistance  as  compared  with  the 
pipe  itself  and  even  when  compared  with  the  surrounding  earth 
in  some  instances.  This  is  particularly  true  of  the  so-called  bell 
and  spigot  pipe  which  is  so  commonly  used  for  large  water  mains. 
At  these  high  resistance  joints  the  current  or  a  portion  thereof 
passes  in  a  shunt  path  through  the  earth  around  the  joint.     This 


Water  Pipe 
Fig.   70. — Current  with  portion  of  pipe  system  bonded  to  rail 


causes  an  eating  away  of  the  iron  on  one  side  of  the  joint  only, 
if  the  current  flow  is  always  in  one  direction.  This  effect  at  the 
joint  is,  of  course,  increased  when  the  pipes  are  connected  with 
the  power  station  by  means  of  copper  conductors  for  the  reason 
that  such  connection  tends  to  increase  the  flow  of  current  in  the 
pipe  line.  Because  of  the  increase  of  electrolysis  at  the  joints  and 
the  impracticability  of  bonding  these  joints,  many  engineers  are 
opposed  to  this  method  of  decreasing  electrolysis. 

Aside  from  the  above  mentioned  methods  of  electrolysis 
reduction,  two  other  plans  have  been  proposed,  although  neither 
has  been  adopted  to  any  extent.  Both  of  these  ])roposed  plans 
invoh-e  the  use  of  the  double  o^■erhead  trolley.     In  one  case  the 


184  ELECTRIC   RAILWAY   ENGINEERING. 

second  trolley  takes  the  place  of  the  rail  return,  the  rest  of  the 
system  remaining  unchanged,  while  in  the  other  plan  the  rail 
becomes  the  neutral  of  the  familiar  three-wire  system.  In  the 
latter  case  a  potential  of  approximately  1200  volts  is  maintained 
between  the  two  overhead  trolley  wires  while  half  this  voltage  is 
impressed  between  either  trolley  and  the  rail.  Obviously  only  the 
current  due  to  unbalanced  load  on  the  two  sides  of  the  three-wire 
system  would  return  to  the  power  station  on  the  rails  and,  as  this 
would  be  a  very  small  portion  of  the  total  in  a  well  planned  sys- 
tem, the  trouble  from  electrolysis  would  be  reduced  considerably. 
With  the  600  volt  two-wire  system,  however,  no  connection  is 
made  between  rails  and  power  station  and  although  there  may  be 
local  currents  in  the  rails  and  earth  in  some  instances,  these  earth 
currents  and  the  electrolysis  resulting  therefrom  are  reduced  to  a 
minimum. 

The  principal  objections  to  these  two  systems  which  have 
probably  prevented  their  general  introduction  may  be  listed  as 
follows : 

High  first  cost. 

High  maintenance  cost. 

Difticulties  in  insulation. 

Complication  at  crossings. 

Greater  overhead  obstruction  of  streets. 
It  is  believed  that  the  above  difficulties  are  self-explanatory  in  a 
system  of  this  type,  involving  as  it  does  the  support  of  two  heavy 
bare  conductors  at  a  distance  of  from  15  to  20  ft.  above  the  street, 
separated  from  each  other  by  a  distance  of  from  12  to  18  in.  and 
maintained  at  a  potential  difference  of  either  600  or  1200  volts. 
No  further  description  of  such  installations  will  therefore  be  given. 
Suffice  it  to  say,  however,  that  although  the  advantages  of  this 
system  from  the  standpoint  of  electrolysis  prevention  were  set 
forth  in  the  very  infancy  of  electric  traction,  there  are  not  more 
than  three  or  four  such  systems  in  operation  in  the  United  States 
today.  Conspicuous  among  these  systems  have  been  the  instal- 
lations at  Cincinnati,  Ohio,  and  Key  West,  Florida. 

Some  municipalities  attempt  to  insure  themselves  against  trou- 
bles from  electrolysis  by  requiring  that  the  fall  of  potential  on  all 
track  return  circuits  be  within  a  certain  predetermined  limit.     For 


ELECTROLYSIS. 


185 


example,  in  rehabilitating  the  electric  railway  systems  in  Chicago 
recently  a  maximum  possible  rail  drop  of  25  volts  was  specified 
by  the  city.  In  order  to  avoid  exceeding  this  limit  with  maximum 
traffic,  negative  return  feeders  were  necessary  and  as  the  distribu- 
tion system  was  largely  underground,  provision  was  made  for 
these  negative  cables  in  the  conduit  lines.  Fig.  71  illustrates 
the  standard  track  construction  adopted  involving  the  use  of 
frequent  cross  bonds  connected  to  the  longitudinal  negative 
return  cables. 

IZ 


^00,000  CM.  Bare  Copper  Caole  (Min.) 
Fig.  71. — Standard  cross  section  of  track  construction  in  Chicago. 

The  above  regulation  is  a  step  in  the  right  direction,  for  it  seeks 
to  remove  the  cause  of  the  trouble,  i.e.,  eliminate  stray  currents, 
rather  than  so  direct  the  existing  stray  currents  that  they  may  do 
no  harm.  If  stray  currents  are  to  be  prevented  or  at  least  reduced 
to  a  minimum,  it  is  necessary  to  reduce  the  resistance  of  the  re- 
turn circuit  as  low  as  possible.  Another  method  which  accom- 
plishes this  same  end  more  completely  is  the  use  of  a  negative 
booster  connected  in  series  with  the  return  circuit  or  often  con- 
nected to  a  single  point  in  the  return  circuit  and  therefore  lower- 
ing the  potential  of  that  point  to  such  a  negative  value  that  the 
current  will  not  leave  the  rail.  In  order  to  do  this  it  is  only  neces- 
sary to  supply  a  low  voltage  heavy  current  generator  driven  by  a 
motor  in  the  substation  with  its  negative  terminal  connected  to  the 
return  circuit  at  the  point  of  greatest  leakage.  This  method  may 
be  likened  to  the  formation  of  a  vacuum  on  a  pipe  line  at  some 
particular  point  in  order  to  draw  the  contents  of  the  pipe  system 
to  that  point  because  of  its  low  absolute  pressure. 

Early  in  this  chapter  the  statement  was  made  that  the  question 
of  electrolysis  has  been  given  decreasing  publicity  by  the  water  and 
gas  companies  since  the  difiicultics  in  connection  therewith  were 
first  made  manifest  in  the  early  nineties.     This  has  taken  place  in 


1 86  ELECTRIC    RAILWAY    ENGINEERING. 

spite  of  the  fact  that  no  complete  cure  has  been  found  for  the 
difficulty.  This  apparently  paradoxical  condition  has  come 
about  largely  because  of  the  increased  activity  on  the  part  of  the 
railway  managements  to  better  inspect  and  maintain  the  track. 
The  value  of  a  low  resistance  return  circuit  is  now  well  known 
among  electric  railway  men  and  by  frequent  testing,  by  replacing 
and  increasing  the  capacity  and  efficiency  of  bonds,  and  by  the 
installation  of  cross  bonds  and  negative  return  conductors,  the 
track  circuit  has  been  placed  in  a  condition  to  return  practically 
all  the  current  to  the  power  station  so  that  the  leakage  by  way  of 
shunt  paths  through  the  earth  and  its  pipe  systems  has  been 
reduced  to  a  minimum. 

In  testing  for  electrolysis  troubles,  methods  similar  to  those 
outlined  in  the  previous  chapter  are  adopted.  As  dangerous 
electrolysis  occurs  only  at  points  where  the  pipes  arc  positive  to 
the  rails,  such  points  are  readily  determined  by  connecting  a 
milli-voltmeter  between  the  rails  and  convenient  points,  such  as 
hydrants  on  the  pipe  lines.  The  positive  pipes  are  then  perma- 
nently connected  to  the  rails  by  means  of  a  copper  bond.  To 
determine  the  actual  current  flowing  in  the  pipes  it  is  only  neces- 
sary to  find  the  fall  in  potential  between  two  convenient  points 
on  the  pipes  at  a  known  distance  apart.  The  resistance  of  the 
pipe  can  usually  be  found  from  tables  or  it  may  be  found  by  test. 
The  current  is  then  calculated  from  Ohm's  law.  That  such 
leakage  currents  are  produced  by  the  railway  system  and  that 
they  vary  with  the  load  on  the  railway  system  is  well  demonstrated 
by  the  tests  plotted  in  Fig.  72  which  represent  readings  of  current 
flowing  in  a  36-in.  water  main  compared  with  the  power  station 
log  of  current  output  during  the  same  period  of  time.  The 
similarity  of  the  two  curves  plotted  with  the  same  abscissae  of  time 
is  rather  surprising. 

In  the  case  of  electrolysis,  therefore,  as  well  as  in  many  other 
difficulties  which  engineers  encounter  from  time  to  time,  it  may  be 
said  that  at  the  time  the  effects  of  this  action  were  first  discovered 
in  Boston  the  problem  looked  most  serious  for  electric  railways 
throughout  the  country  and  many  suits  were  brought  by  water, 
gas,  and  telephone  companies  against  the  railway  companies  for 
damage  to  pipe  lines,  etc.,  the  test  case  at  Peoria,  Illinois,  which 


ELKCTROI.YSIS. 


187 


railway  men  have  been  following  most  closely,  being  still  unde- 
cided after  years  of  controversy.  The  problem  has  been  studied 
carefully,  however,  and  such  means  of  reducing  its  serious  effects 


Fig. 


devised  that  while  it  can  never  be  entirely  eliminated,  it  may  be 
said  that  its  results  are  no  longer  serious,  if  careful  and  persistent 
testing  and  bonding  be  the  policy  of  the  railway  company. 


CHAPTER  VIII. 
Signal  and  Dispatching  Systems. 

The  problem  of  dispatching  cars  and  of  protecting  one  car 
from  another  on  the  same  section  of  track  is  largely  confined  to 
interurban  systems,  for  in  the  case  of  city  railways,  speeds  are 
low,  the  headway  is  small,  and  double  tracks  are  commonly  in  use. 
Cars  are  therefore  usually  operated  as  closely  as  possible  on  a 
predetermined  schedule  by  the  car  crews  and  considerable  respon- 
sibility is  placed  upon  them  for  the  regaining  of  schedule  time  in 
case  of  delay.  In  many  cities  branch  line  dispatching  is  done 
by  a  starter  stationed  in  the  city  square  or  at  the  junction  point 
of  branch  line  and  the  main  tracks .  For  the  above  reasons,  there- 
fore, this  chapter  will  be  principally  devoted  to  interurban  systems, 
although  the  possible  application  of  a  number  of  the  signal  systems 
to  urban  car  operation  will  be  obvious. 

A  complete  system  of  train  dispatching  by  a  single  dispatcher 
for  the  entire  road  does  away  to  a  large  extent  with  the  necessity 
of  signals  other  than  those  under  the  control  of  the  dispatcher 
installed  for  the  purpose  of  attracting  the  attention  of  a  train 
crew  for  special  orders  while  enroute,  or  to  stop  a  car  in  case  of  an 
error  in  orders  discovered  after  the  last  communication  with  the 
crew.  Most  of  the  signal  systems  are  therefore  operated  in 
conjunction  with  a  dispatching  system  and  act  as  a  check  there- 
upon. Some  of  the  more  complete  systems,  however,  are  operated 
with  little  attention  from  the  dispatcher  and  the  complete  auto- 
matic block  signal  system  on  a  double  track  road  may  be  practi- 
cally independent  of  dispatcher's  orders. 

Where  a  dispatching  system  is  adopted,  those  signals  commonly 
used  in  steam  railroad  practice  are  occasionally  found  on  electric 
lines,  involving  the  manually  operated  signals  and  telegraphic 
train  orders  to  way  station  agents.  Even  the  "staff"  system 
which  is  used  extensively  in  England  may  occasionally  be  found. 
This  is  really  a  combined  signal  and  dispatching  system  consisting 


SIGNAL  AND    DISPATCHING    SYSTEMS.  189 

of  two  electrically  interconnected  mechanisms,  one  at  either  end 
of  a  block,  which  permit  a  staff  to  be  removed  therefrom  if  there 
be  no  train  in  the  block  ahead.  A  second  staff  cannot  be  removed 
from  either  of  the  terminal  stations  until  the  mJssing  staff  has 
been  replaced  at  the  farther  end  of  the  line.  This  system  not 
only  protects  the  block  but  also  gives  the  train  crew  tangible 
evidence  that  they  have  the  right  of  way  in  the  block. 

The  dispatching  system  most  common  to  electric  railways  is 
that  using  the  telephone  for  communication  between  dispatcher 
and  train  crew.  Telephone  booths  are  either  provided  at  sidings 
or  a  portable  telephone  is  carried  on  each  car  which  may  be 
readily  connected  with  the  telephone  circuit  paralleling  the  track 
by  means  of  a  flexible  cable  and  two-pole  plug  switch.  It  is  cus- 
tomary to  require  the  motorman  to  receive  the  orders  and  write 
same  on  an  order  blank  which  furnishes  a  carbon  copy  for  the 
conductor.  The  order  is  checked  by  the  conductor  reading  from 
the  carbon  copy  to  the  dispatcher  over  the  telephone.  This 
check  message  is  either  ok'd  or  corrected  by  the  dispatcher. 
Whereas  there  are  m.any  modifications  of  this  method  in  use, 
the  telephone  is  very  generally  adopted  and  has  proved  very 
satisfactory.  In  fact  several  of  the  steam  railroad  trunk  lines 
have  adopted  the  telephone  in  place  of  the  telegraph  for  train 
dispatching. 

Such  telephone  lines  should  be  constructed  for  dispatching  only, 
the  business  to  be  transacted  between  other  officials  or  depart- 
ments of  the  road  being  provided  for  by  another  line.  This 
duplicate  line  is  fully  warranted  in  the  interests  of  safety  and  the 
avoidance  of  train  delays.  Care  should  be  taken  also  to  insist 
upon  the  repeating  of  orders,  for  serious  wrecks  have  occurred 
due  to  the  train  crew  receiving  but  a  portion  of  the  order  or  mis- 
taking an  order  given  to  a  crew  at  the  dispatcher's  office  with  the 
receiver  off  the  hook  for  an  order  intended  for  them.  Repeating 
an  order  will  correct  these  errors. 

Aside  from  the  telephone  order  and  the  possible  stop  signals, 
mentioned  above,  which  may  be  under  the  control  of  the  dis- 
patcher, some  railway  companies  provide  a  means  at  the  disposal 
of  the  dispatcher  for  shutting  off  power  from  any  desired  section 
of  trolley  in  order  to  prevent  a  wreck  in  case  of  emergency.     Still 


IQO 


ELECTRIC    RAILWAY    ENGINEERING. 


Other  officials  believe  this  to  be  a  dangerous  tool  in  the  hands  of 
the  dispatcher  upon  which  he  may  tend  to  rely  too  frequently. 
Such  a  device  applied  to  the  feeder  circuit  breakers  on  the  power 
station  switchboard  is  illustrated  in  Fig.  73.  In  this  case  the 
tripping  device  is  operated  by  a  relay  which  is  supplied  with 
current  from  the  trolley  with  a  number  of  incandescent  lamps  in 
series  and  with  the  controlling  switch  in  the  dispatcher's  office. 
This  particular  device  is  used  by  the  Indianapolis  and  Louisville 
Traction  Company.  In  making  use  of  this  device  it  should  be 
remembered  that  it  does  not  necessarilv  enable  the  car  to  be 


Fig.   7^ 

stopped  at  once,  for  in  the  case  of  high-speed  interurban  roads  the 
cars  may  travel  for  considerable  distances  at  high  speeds  without 
the  use  of  power.  When  the  lighting  circuit  is  not  in  use  there  is 
no  indication  to  the  car  crew  that  the  power  has  been  shut  off. 

Signal  Systems. — Returning  to  the  signal  systems  which 
usually  augment  but  may  replace  the  dispatching  system,  it  may 
be  §aid  that  the  present  systems  have  been  a  gradual  growth  from 
the  single  incandescent  five  lamp  series  circuit  between  trolley 
and  ground  to  the  more  elaborate  automatic  block  signals  similar 
to  those  used  on  steam  roads  which  are  now  being  rapidly  adopted 
by  the  large  interurban  railroads. 


SIGNAL   AND    DISPATCHING    SYSTEMS. 


191 


For  protection  against  accidents  and  in  order  that  the  schedule 
may  be  maintained,  it  is  desirable  that  the  train  crew  should 
know  upon  entering  a  block  or  certain  section  of  the  road 

1.  Whether  there  is  another  car  in  the  block. 

2.  How  many  cars  there  are  in  the  block. 

3.  What  direction  the  cars  are  going. 

The  latter  requirement  is,  of  course,  applicable  to  single  track 
roads  only.  As  a  matter  of  fact,  nearly  all  signals  are  confined 
to  the  first  case  only  or  the  first  and  third  classes,  but  verv  few  in 

Trnlley 


U 

-C-0-| 


a       1, 


G^r 


G  ^^ 


F"iG.  74. — Simple  lamp  signal. 


general  use  answer  the  second  (question.  In  cjrder  to  do  this 
automatically  the  circuits  have  become  too  complex,  involving 
difficulties  and  excessive  expense  in  their  maintenance.  Signals 
displayed  on  the  cars  are  used  to  signify  that  another  car  is  follow- 
ing in  the  same  block. 

Probably  the  most  simple  arrangement  used  as  a  signal,  and  one 
to  which  several  roads  have  returned  after  trying  out  the  more 
nearly  automatic  types,  is  that  shown  in  Fig.  74.  This  consists 
of  a  series  of  five  incandescent  lamps  connected  as  shown  by  means 
of  a  double-throw  switch  between  trolley  and  ground,  two  of  each 
group  being  located  at  one  end  of  the  block  and  three  at  the  other. 
The  group  of  three  lamps  is  placed  behind  a  white  or  green  lens 
and  the  two  lamp  group  provided  with  a  red  lens.  Upon  en.er 
ing  the  block  the  circuit  is  closed  by  means  of  the  switch  which 
lights  a  red  light  at  the  opposite  end  and  a  white  or  green  light  at 
the  entering  end.  Upon  arrival  at  the  other  end  of  the  block  \\\v 
lights  may  be  switched  out  and  the  circuits  are  such  that  the  lights 


192 


ELECTRIC   RAILWAY   ENGINEERING. 


may  then  be  lighted  from  either  end.  An  extra  circuit  duplicating 
that  of  Fig.  74  should  be  provided,  however,  for  operation  in  both 
directions.  The  advantages  of  this  signal  are  its  simplicity  and 
the  necessity  of  one  of  the  crew  leaving  the  car,  when  stopped,  to 
operate  the  signal  switch.  Its  disadvantages  are  that  the  signal 
light  may  be  extinguished  and  the  signal  reversed  from  either  end 
with  a  car  still  in  the  block  and  if  the  switch  be  accidentally  left 
in  the  off  position  the  signal  cannot  be  operated  from  the  other  end. 
Elaborating  upon  this  principle  and  adding  the  automatic 
feature,  the  United  States  Signal  Company  has  developed  a  signal 


rO 
GO 

12     3      4 


Trolley 


R  O 

GO 

12     3     4 


Fig.  75. — United  States  signal. 


for  single  track  blocks  which  has  been  adopted  by  many  roads. 
It  operates  from  the  trolley  circuit  and  consists  of  one  signal  box 
and  trolley  switch  at  either  end  of  the  block  connected  as  in  Fig. 
75  and  requiring  two  wires  throughout  the  length  of  the  block.  A 
car  entering  the  block  at  (A)  makes  a  momentary  connection  be- 
tween the  trolley  wire  and  wire  No.  4,  as  the  trolley  wheel  operates 
the  iron  tongue  switch  mounted  on  the  trolley  wire.  This  momen- 
tary connection  closing  a  circuit  to  ground  through  a  relay  and  a 
suitable  resistance,  completes  the  permanent  circuit  connecting 
the  trolley  wire  through  No.  i,  the  green  lamp  at  (A),  the  signal 
line  wire,  the  red  lamp  at  (B),  through  resistance  in  box  (B)  to 
ground.  Other  cars  entering  at  (A)  do  not  change  the  signal  set- 
ting, but  a  tar  leaving  the  block  at  (B)  energizes  wire  No.  5  through 
the  agency  of  the  overhead  trolley  switch  and  trips  the  relay  which 


SIGNAL  AND    DISPATCHING    SYSTEMS.  1 93 

extinguishes  the  red  light.  A  car  entering  at  (B)  performs  the 
reverse  operation,  lighting  the  green  light  at  (B)  and  the  red  signal 
at  (A).  The  boxes  and  switches  are  therefore  interchangeable. 
Red  and  green  disks  are  displayed  in  some  types  of  this  signal  for 
day  use,  although  the  lights  are  commonly  used  as  day  signals  as 
well.  This  type  of  signal  has  given  a  fair  degree  of  satisfaction 
although  its  maintenance  expense  is  high,  especially  because  of 
damage  by  lightning.  In  fact  it  is  very  difficult  to  design  a  signal 
operating  upon  a  grounded  circuit  which  will  not  be  seriously 
affected  by  lightning.  The  widely  varying  voltages  on  the  various 
sections  of  the  average  interurban  line  also  introduce  difficulties 
in  the  design  of  signals  to  be  operated  from  the  trolley  circuit. 
It  should  be  noted  that  in  both  of  the  above  systems  the  motor- 
man  is  assured  that  the  red  signal  has  been  displayed  at  the  farther 
end  of  the  block  if  the  green  light  appears  at  the  entering  end. 
This  fact  is  seldom  determined  by  the  steam  railroad  engineer 
who  relies  upon  the  automatic  block  signal  to  give  the  danger  indi- 
cation without  actually  observing  the  signal  movement  himself. 

A  signal  system  very  similar  to  the  above  is  manufactured  by 
the  Nachod  Signal  Company.  In  addition  to  the  above  protec- 
tion, however,  this  signal  counts  the  cars  into  the  block  as  they 
enter  and  does  not  return  to  "clear"  until  each  car  has  been 
counted  out.  An  indication  is  given  the  motorman  by  means  of 
the  flash  of  a  lamp  that  his  car  has  been  registered  as  the  trolley 
switch  is  passed  although  the  signal  aspect  remains  unchanged. 
A  further  protection  is  offered  in  this  system  in  that  the  signal 
may  be  made  an  "absolute  block"  system  by  manually  opening 
one  of  the  line  wires  by  means  of  a  pole  switch,  thus  causing  red 
signals  to  be  displayed  at  both  ends.  This  provision  is  of  conve- 
nience when  a  line  repair  crew  is  working  in  the  block. 

Still  another  type  of  signal  similar  to  the  above  displays  an 
orange-colored  light  when  no  car  is  in  the  block  and  a  green 
cautionary  light  as  the  car  enters  in  series  with  the  red  danger 
signal  at  the  distant  end.  The  principal  difference  in  the  opera- 
tion of  this  signal  is  that  it  makes  use  of  a  single  rail  with  each 
block  insulated  from  its  neighbor  as  far  as  the  flow  of  signal  cur 
rent  is  concerned,  as  will  be  explained  later  in  connection  with 
single  rail  automatic  block  signals. 
13 


194  ELECTRIC    RAILWAY   ENGINEERING. 

Automatic  Block  Signals. — The  signals  described  thus  far 
have  been  installed  on  sections  of  single  track  between  sidings  to 
control  and  protect  cars  operating  in  both  directions.  In  distinct 
contrast  to  these  is  the  automatic  block  signal  used  to  protect  cars 
on  sections  of  double  track  from  the  danger  of  operation  with  too 
small  headway  and  yet  to  permit  the  minimum  safe  headway  to 
be  maintained  under  conditions  of  heavy  traffic.  This  is  the 
type  of  signal  used  to  an  ever  increasing  extent  on  steam  trunk 
lines,  although  the  details  of  design  vary  somewhat  when  applied 
to  electric  service.  While  the  large  interurban  systems  of  the 
Middle  West  are  just  beginning  to  consider  seriously  the  question 
of  equipping  their  lines  with  automatic  block  signals,  this  type 
of  signal  has  for  a  long  time  found  a  most  important  application 
in  elevated  and  subway  installations  in  the  largest  cities  of  the 
country.  A  rather  detailed  study  of  this  type  of  signals,  therefore, 
is  very  appropriate  at  this  time. 

A  "block"  as  the  term  is  used  in  this  discussion,  may  be 
defined  as  a  section  of  track  so  protected  that  but  one  train  can  be 
in  that  section  at  any  given  time,  no  other  train  being  allowed  to 
enter  until  the  last  truck  of  the  previous  train  has  left  the  section. 
The  length  of  these  protected  blocks  will  be  determined  in  each 
particular  case.  They  must  be  sufficiently  long  to  enable  a 
heavy  high-speed  train  to  stop  within  their  limits  and  yet  suffi- 
ciently short  to  permit  the  smallest  safe  headway  between  trains 
during  rush  hours.  They  usually  vary  from  2000  ft.  to  2  miles 
in  length. 

At  the  entrance  to  each  block  a  signal  must  indicate,  both  by 
day  and  night,  whether  or  not  there  is  a  train  in  the  first  block 
beyond.  Such  a  signal  is  termed  the  "home"  signal.  In  addi- 
tion it  has  been  found  advisable,  if  high  speed  trains  are  to  operate 
smoothly  without  frequent  periods  of  slow-down,  to  install  an 
additional  signal,  usually  upon  the  same  standard  as  the  home 
signal,  to  indicate  the  condition  of  the  second  block  ahead.  This 
signal  is  termed  the  "distant"  signal. 

These  indications  are  usually  given  in  daylight  by  means  of  a 
semaphore  and  with  colored  lights  at  night.  As  considerable 
trouble  has  been  experienced  from  the  use  of  colored  "bulls- 
eyes"  or  signal  "roundels"  at  night  upon  roads  using  the  very 


I 


SIGNAL  AND    DISPATCHING    SYSTEMS.  1 95 

powerful  headlights  owing  to  reflections  from  unlighted  roundels 
appearing  as  signals,  it  is  believed  that  if  the  more  powerful 
headlight  is  adopted  the  semaphore  or  "position"  signal  will  be 
ultimately  very  generally  used  as  a  night  signal  as  well,  being 
sufficiently  well  illuminated  by  means  of  the  headlight  to  permit 
the  accurate  reading  of  signal  aspects/  The  semaphore 
when  in  a  horizontal  position  indicates  "danger,"  while  the 
"proceed,"  or  "clear"  signal  is  usually  indicated  by  a  60°  angle 
in  the  lower  quadrant.  In  some  types  of  signals  three  angular 
positions  are  used,  a  45°  position  indicating  "caution"  and  a 
vertical  position  "proceed"  or  "clear"  aside  form  the  "danger" 
indication.  In  a  few  instances,  and  upon  the  Pennsylvania 
railroad  in  particular,  the  "clear"  position  is  represented  with 
the  semaphore  in  the  upper  quadrant,  the  arm  falling  to  the  hori- 
zontal position  by  gravity  to  indicate  "danger"  or  when  anything 
is  wrong  with  the  signal  apparatus.  Such  a  signal  is  designated 
as  a  "normal  danger"  signal  as  contrasted  with  the  "normal 
clear"  types  described  above.  Each  has  its  rather  obvious  ad- 
vantages and  disadvantages  and  therefore  its  ardent  supporters 
among  signal  engineers.  The  corresponding  signals  at  night  are 
usually  red  for  "danger,"  green  for  "clear"  and  yellow  for 
"caution,"  although  the  two  latter  colors  vary  somewhat  for  the 
different  roads. 

As  the  train  arrives  at  the  entrance  of  a  block  the  home  signal 
denotes  the  condition  of  the  first  block  and  the  distant  signal  that 
of  the  second  block  ahead.  With  both  at  "danger"  the  two 
blocks  ahead  are  occupied  and  the  train  stops.  With  the  home 
signal  at  "clear"  and  the  distant  signal  at  "danger,"  the  first 
block  is  clear  and  the  second  occupied.  The  train  may  enter  the 
block  under  control.  With  both  signals  at  "clear"  the  engineer 
knows  that  two  blocks  ahead  at  least  are  clear  and  he  may  enter 
the  block  at  full  speed.  The  distant  signal  at  the  first  block  and 
the  home  signal  of  the  second  block  are  so  interlocked  that  the 
former  cannot  move  to  "clear"  until  the  latter  has  attained  a 
similar  position.  Upon  entering  the  first  l)lock  under  control 
with  the  distant  signal  at  "danger"  it  is  expected  that  the  next 

'  "Headlight  tests"  by  Professors  C.  F.  Harding  and  A.  N.  Topping,  A.  I.  E.  E., 
Vol.  XXDC. 


196  ELECTRIC   RAILWAY   ENGINEERING. 

home  signal  will  be  at  "danger,"  Since,  however,  the  signal 
may  have  changed  before  the  train  reaches  the  second  block,  it  is 
often  advisable  to  install  a  second  distant  signal  within  safe  stop- 
ping distance  of  the  second  block.  This  is  especially  true  if  the 
second  block  signal  is  not  readily  seen  at  some  distance,  since  it 
avoids  slowing  down  if  the  second  block  has  been  cleared  in  the 
meantime. 

While  it  is  unnecessary  to  describe  in  detail  the  operating 
mechanism  of  the  semaphore  and  colored  roundels  in  its  various 
forms,  it  may  be  said  that  this  movement  is  accomplished  by 
means  of  mechanical  levers  and  bell  cranks,  gas  or  air  pressure 
operating  pistons  in  cylinders  located  in  the  base  of  the  signal,  or 
by  electricity  used  through  the  agency  of  a  solenoid  or  series 
motor.  The  control  of  the  local  apparatus  at  the  signal  by  means 
of  electric  relay  circuits  is,  however,  of  greatest  importance  and 
will  be  explained  in  detail. 

Steam  Railroad  Practice. — As  the  block  signal  systems  used 
with  electric  roads  have  been  patterned  after  the  more  simple 
steam  railroad  installations  a  description  of  the  latter  will  aid  in 
understanding  the  former.  The  two  rails  for  a  block  in  length 
are  insulated  from  one  another  and  also  from  the  adjacent  rails 
of  neighboring  blocks  by  means  of  insulating  rail  joints.  The 
various  rail  lengths  of  a  single  block  are  bonded  together  in  a 
manner  similar  to  that  described  in  Chapter  VI,  but  with  much 
smaller  wire  bonds.  A  gravity  or  storage  battery  of  i  or  2  volts 
e.  m.  f.,  located  in  a  manhole  below  the  frost  line,  is  connected 
between  the  rails  at  one  end  of  the  block.  At  the  other  end  of 
the  block  a  sensitive  relay  is  connected  across  the  two  rails.  This 
relay  is  usually  mounted  in  the  base  of  the  signal  tower  and 
thereby  protected  from  the  weather.  Where  there  is  no  train  in 
the  block  the  battery  supplies  current  to  the  relay  by  way  of  the 
two  rails  and  the  signal  is  held  in  the  "clear"  position.  As  the 
first  trucks  of  a  train  enter  the  block,  however,  the  wheels  and 
axles  short-circuit  the  relay  and  it  opens,  closing  the  local  circuit 
which  throws  the  semaphore  and  colored  roundels  into  the  "dan- 
ger" aspect.  The  signal  is  locked  in  this  position  until  the 
movement  of  the  last  truck  of  the  departing  train  from  the  block 
removes  the  short  circuit,  closes  the  relay,  and  clears  the  signal. 


SIGNAL   AND    DISPATCJIING    SVSTKMS. 


197 


Such  is  the  very  simple  circuit  and  mechanism  of  the  automatic 
block  signal  for  steam  railroads  and  although  its  first  cost  has 
been  sufficiently  high  to  render  its  adoption  rather  slow,  its  main- 
tenance is  not  excessive  and  its  positive  operation  is  to  be  depended 
upon.  In  fact  in  one  instance  but  one  failure  to  operate  in 
250,000  was  the  record  of  operation  on  a  large  signal  system 
during  the  period  of  one  year. 

Electric  Railroad  Block  Signals. — With  the  electric  railroad, 
which  makes  use  of  the  track  rails  for  the  return  of  heavy  currents 
to  the  substation  or  power  house,  the  problem  becomes  a  more 
difficult  one,  as  the  rails  are  no  longer  free  for  sectional  insulation 


Trollej-  or  Third  Rail 


3^SH 


D.C.  Railway 
Generator 
Ret  urn  Rail         j.  — 


Si, 
Sijsiial  Lig-iit 


Blocli  Rail 


&a 


vwvJ 


Fuse  - 
Non.inductive. 
Resistance 
Reactance  Coil 

Track     _» 
Transformer 

— A.C.  Track 
—J     Relay 


Jru 


lil  Insulation 


-"yy— I  Signal  A.C. 
^="^"^nJ  Generator 


A.C.  Signal  Mains 


Tjf\ 


Fig.   76. — Single  rail  alternating  current  block  signal. 

as  in  the  case  of  steam  roads.  One  method  of  overcoming  this 
difficulty  which  would  naturally  suggest  itself  is  to  use  one  rail 
for  signal  purposes  and  the  second  rail  for  the  return  of  power 
current.  The  further  use  of  alternating  current  for  the  signal 
relay  would  permit  selective  operation  of  the  latter  without  inter- 
ference from  the  power  current.  Such  a  system  is  successfully 
used  in  the  New  York  subway,  its  principle  of  operation  being 
illustrated  by  Fig.  76. 

By  referring  to  the  above  figure  it  will  be  seen  that  one  rail 
termed  the  "block  rail"  is  insulated  in  sections,  one  block  in 
length,  constituting  a  circuit  for  signal  current  only.  The  other 
rail  carries  the  current  from  the  trains  and  also  acts  as  a  common 
return  circuit  for  the  signal  system.  Alternating  current  for  the 
signal  circuit  and  also  for  the  signal  lamps  is  supplied  through 


198 


ELECTRIC   RAILWAY   ENGINEERING. 


transformers  from  single-phase  alternating  current  mains  paral- 
leling the  track.  If  the  power  current  is  flowing  in  the  return 
rail  from  left  to  right  the  voltage  between  rails  at  (B)  will  be 
slightly  less  than  at  (A)  due  to  the  fall  of  potential  in  the  rail. 
This  will  cause  some  of  the  direct  current  to  pass  through  the 
relay  connected  between  the  rails  at  (A),  thence  through  the 
block  rail  and  the  transformer  secondary  to  the  return  rail  at  (B), 
the  latter  forming  a  high  resistance  shunt  path  to  the  length  of 
return  rail  (AB).  In  order  to  limit  the  amount  of  this  current 
which  would  otherwise  produce  a  uni-directional  magnetic  field 


Fig. 


in  the  relay  and  transformer,  high  noninductive  resistances  are 
inserted  in  series  with  the  relay  and  transformer  secondary  and 
a  reactance  coil  shunted  across  the  relay.  While  the  direct 
power  current  following  the  block  rail  will  pass  freely  through  this 
reactance,  the  signal  alternating  current  will  be  prevented  by  the 
impedance  of  the  reactance  coil  from  taking  that  path  and  will 
therefore  pass  through  the  relay.  As  an  additional  precaution 
in  the  case  of  the  transformer  an  air-gap  is  introduced  into  the 
magnetic  circuit  to  reduce  to  a  minimum  any  magnetic  flux 
which  might  be  produced  by  the  relatively  small  leakage  direct 
current. 


SIGNAL  AND    DISPATCHING    SYSTEMS.  1 99 

With  these  added  precautions  the  relay  system  operates  exactly 
as  in  the  case  of  steam  railroad  equipments  with  the  exception 
that  the  relay  must  be  of  the  alternating  current  type.  A  relay 
depending  upon  the  torque  produced  by  eddy  currents  induced 
in  an  aluminum  disc  being  acted  upon  by  the  magnetic  field  set 
up  by  the  current  in  the  relay  has  been  adopted  for  this  purpose. 

In  the  case  of  the  particular  installation  of  this  system  in  the 
New  York  subway,  the  alternating  current  distribution  is  at 
500  volts  and  60  cycles,  the  track  transformers  stepping  the  po- 
tential down  to  ID  volts,  while  the  signal  lamps  are  operated  at 
55  volts.  The  resistance  of  the  track  and  signal  circuit  is  such 
as  to  impress  approximately  five  volts  upon  the  relay.  The  power 
factor  of  the  circuit  is  in  the  neighborhood  of  80  per  cent,  and 
the  power  taken  by  an  average  block  but  80  watts.  A  typical 
installation  is  represented  in  Fig.  77. 

Block  Signals  for  Alternating  Current  Roads. — When  the 
problem  arose  to  equip  electric  roads  operating  with  alternating 
current  in  the  track  rails,  it  may  be  readily  seen  that  still  further 
difliiculties  were  encountered.  The  problem  was  fairly  well 
solved,  however,  by  the  development  of  the  two  rail  signal  system 
making  use  of  inductive  bonds,  although  this  equipment  can 
hardly  be  considered  in  a  state  of  perfection  as  yet.  It  has  been 
adopted  as  well  in  some  instances  on  direct  current  roads  where 
the  full  conductivity  of  the  two  rails  was  considered  of  sufficient 
value  to  overcome  the  slight  disadvantages  of  a  system  requiring 
the  use  of  inductive  bonds. 

The  principle  of  this  type  of  signal  system,  similar  to  that 
operating  on  the  single-phase  terminal  electrification  of  the 
New  York,  New  Haven  and  Hartford  Railroad  in  New  York, 
is  illustrated  in  Fig.  78.  It  will  be  seen  that  each  rail  is  insulated 
at  the  ends  of  the  block  as  in  the  case  of  steam  railroad  practice, 
but  inductive  bonds  are  installed  between  the  rails  at  (AB)  and 
(EF)  of  suflicient  capacity  to  carry  the  train  current.  The 
middle  points  of  adjacent  bonds  are  connected  together  so  that 
there  is  a  complete  electrical  circuit  from  train  to  power  house  by 
way  of  each  rail,  this  circuit  invohing  one-half  of  each  bond  at 
every  block.  These  bonds  arc  carefully  designed  so  that  their 
counter  e.  m.  f.  will  not  be  great  at  the  frequency  of  25  cycles  or 


200 


ELECTRIC    RAILWAY    ENGINEERING. 


below,  at  which  the  train  motors  operate,  but  will  be  sufficiently 
great  to  produce  a  useful  difference  of  potential  between  the  rails 
in  the  signal  circuit  which  is  operated  at  60  cycles.  In  other 
words  a  very  interesting  application  is  made  of  the  theory  that 
the  reactance  of  a  coil  is  proportional  to  the  frequency  and  the 
bonds  are  therefore  designed  to  operate  upon  one  frequency  only. 
The  immediate  source  of  power  is  the  transformer  as  in  the 
single  rail  system,  but  in  this  case  the  power  current  is  sufficiently 
well  balanced  in  the  two  rails  to  prevent  unbalanced  currents 
flowing  in  the  transformer  and  the  air  gap  in  the  magnetic  circuit 

Trolley 


Fig.  78. — Double  rail  alternating  current  block  signal  using  inductive  bonds. 

is  therefore  omitted.  The  transformer  is  designed  with  a  rela- 
tively high  leakage  factor,  however,  in  order  that  the  current  may 
not  be  excessive  when  the  secondary  of  the  transformer  is  short 
circuited  by  the  train  in  the  block.  It  will  be  noted  further  that 
for  the  above  reasons  the  auxiliary  resistances  and  reactance 
shunt  across  the  relay  may  be  omitted. 

With  these  changes  and  a  slight  change  in  the  design  of  the 
relay,  the  system  operates  as  in  the  single  rail  design.  The 
direction  of  the  power  current  is  shown  by  full  lines  and  that  of 
the  signal  current  by  dotted  lines  in  Fig.  78. 

In  all  of  the  above  automatic  block  systems  it  should  be  noted 
that  if  the  track  relay  circuit  be  opened  the  action  is  the  same  as 
though  the  relay  were  short  circuited  by  a  train  in  the  block,  i.e., 
the  signal  is  thrown  to  "danger."  This  action  has  proved  of 
great  value  in  detecting  broken  rails  and  has  probably  prevented 
a  number  of  wrecks  thereby. 


SIGNAL  AND    DISPATC11IN(;    SYSTEMS.  20I 

In  a  few  instances  this  type  of  signal  has  been  used  on  single 
track  blocks,  but  here  the  difficulty  lies  in  not  being  able  to  tell 
which  way  the  train  is  moving  that  is  occupying  the  block,  while 
in  the  double  track  system,  if  the  block  were  not  cleared  in  the 
usual  time,  the  train  might  move  forward  slowly  in  order  to  locate 
the  trouble,  with  the  knowledge  that  the  train  ahead  was  headed 
in  the  same  direction.  In  the  case  of  the  single  track,  however, 
it  would  be  necessary  to  send  a  flag-man  ahead  to  prevent  a 
head-on  collision  if  such  an  investigation  were  attempted.  It  is 
probably  for  this  reason,  together  with  the  larger  percentage  cost 
of  block  signals,  that  they  have  not  been  widely  installed  on  single 
track  roads.  Upon  the  Harriman  lines,  however,  where  they 
have  been  used  to  a  considerable  extent  on  single  track  it  is  claimed 
that  their  detection  of  broken  rails  as  above  explained  has  well 
warranted  their  installation. 

Cost. — The  Electric  Journal  is  authority  for  the  statement  that 
the  average  cost  of  an  automatic  block  signal  system,  with  com- 
bined home  and  distant  signals  on  a  single  standard  will  vary 
from  S750  to  $1100  per  block,  depending  upon  the  length  of 
block,  number  of  switches,  and  method  of  signal  control.  An 
average  value  for  maintenance  has  been  placed  at  from  $75  to 
$100  per  annum  for  a  two-arm  signal. 

It  may  have  been  inferred  from  the  previous  discussion  that 
there  is  a  wide  variety  of  signal  systems  with  widely  var}'ing  de- 
grees of  protection  and  corresponding  first  costs,  from  which  to 
choose.  While  a  theoretically  perfect  system  has  not  yet  been 
developed,  it  is  safe  to  say  that  the  more  complete  systems  have 
not  been  cast  aside  by  the  interurban  railroads  because  of  their 
unsatisfactory  design  and  operating  qualities,  but  rather  because 
of  their  high  first  cost  and  maintenance  charges.  As  the  com- 
bined result  of  some  rather  serious  wrecks  which  have  recently 
taken  place  on  interurban  roads,  the  advertising  value  of  a  com- 
plete automatic  block  signal  system  and  the  increasing  pressure 
which  is  being  brought  to  bear  by  state  railroad  commissions 
throughout  the  country,  it  is  believed  that  the  automatic  block 
signal  will  be  pretty  generally  adopted  in  the  near  future  and  the 
resulting  developments  in  the  electric  signal  field  correspondingly 
rapid. 


PART  III. 

EQUIPMENT. 


CH.\PTER  T. 
Track  Layout  and  Construction. 

The  electrical  engineer  of  a  proposed  electric  interurban  rail- 
way is  often  called  upon  to  determine  the  right  of  way  and  super- 
intend the  track  survey  and  construction,  although  in  the  large 
city  systems  or  extensive  interurban  developments  a  technically 
trained  civil  engineer  is  usually  given  this  responsibility.  In 
either  case  the  electrical  engineer  should  be  familiar  with  such 
general  features  of  the  problem  as  may  be  herein  outlined. 

Right-of-way. — After  several  proposed  routes  have  been 
suggested  for  the  new  railway,  possibly  with  the  aid  of  rough 
preliminary  surveys  for  each,  and  detailed  notes  taken  of  the 
advantages  and  disadvantages  of  each,  involving  the  typography 
of  the  country,  number  of  intermediate  towns  and  amount  of 
tributary  population  served,  possible  schedules,  etc.,  it  is  neces- 
sary to  decide  upon  one  route.  This  is  usually  determined  by 
the  officials  of  the  company  in  conference  with  the  engineer. 
With  this  decision  in  mind  the  problem  of  obtaining  the  right-of- 
way  presents  itself  and  it  is  often  policy  not  to  make  the  above 
decision  public  until  after  the  greater  portion  of  the  right-of-way 
has  been  secured.  In  fact  it  has  sometimes  been  found  advisable 
to  propose  publicly  two  possible  routes  and  even  go  to  the 
extent  of  purchasing  options  on  land  along  each  in  order  that  an 
element  of  competition  may  enter,  preventing  land  and  options 
from  assuming  exhorbitant  values  along  the  desired  route. 

Great  diplomacy  must  be  exercised  by  the  advance  real  estate 
agent  in  order  to  secure  the  desired  route  at  a  reasonable  figure 
and  without  too  many  concessions,  which  often  complicate  the 
schedules  and  embarrass  the  company  when  operation  begins. 
It  must  always  be  remembered  that  much  of  the  future  traffic  will 
come  from  those  with  whom  these  preliminary  negotiations  are 
made. 

If  satisfactory  locations  cannot  be  secured,  either  because  of 

20n 


2o6  ELECTRIC    RAILWAY    ENGINEERING. 

opposition  to  the  proposed  road  or  too  high  prices  being  placed 
upon  the  land,  right  of  eminent  domain  may  be  secured  through 
the  court  and  certain  sections  of  the  route  condemned  and  thereby 
purchased  at  a  value  appraised  by  the  court  or  a  commission 
appointed  by  the  court.  As  this  proceeding  makes  public  the 
proposed  route  and  prejudices  some  against  the  company,  it 
should  be  avoided  if  possible,  but  if  found  necessary,  it  should  be 
postponed  until  the  remainder  of  the  land  has  been  secured. 

It  will  be  noted  that  the  above  discussion  presupposes  a  private 
right-of-way  for  the  road.  Such  a  route  is  generally  much  to  be 
preferred  except  within  the  limits  of  intermediate  towns,  and  even 
in  the  latter  case  a  route  but  a  few  blocks  from  the  center  of  town 
on  a  back  street  with  little  trafhc,  where  speeds  may  be  fairly 
high  and  frccjuent  curves  avoided,  should  be  given  serious  con- 
sideration. In  some  instances  interurban  railroads  run  for  miles 
along  country  roads,  but  it  is  usually  done  at  the  expense  of  low 
schedule  speeds,  and  high  maintenance  charges  due  to  restric- 
tions often  imposed  by  town  boards  and  street  commissioners,  not 
to  mention  frequent  and  serious  accidents.  A  slightly  larger  first 
cost  for  a  private  right-of-way  is  justified  in  most  cases  from  the 
standpoints  of  schedule,  safety  and  independence  from  ordi- 
nances stipulated  by  outsiders  not  only,  but  from  the  purely  finan- 
cial consideration  as  well. 

A  right-of-way  at  least  loo  ft.  in  width  should  be  secured  to 
allow  for  possible  double  track  with  necessary  cuts  and  embank- 
ments provided  with  adequate  drainage  ditches.  Such  a  strip 
of  land  averages  twelve  acres  to  the  mile. 

With  the  route  approximately  determined  and  the  right-of- 
way  secured,  a  final  survey  should  be  made  to  locate  the  exact 
line  for  the  track  and  to  determine  the  profile.  With  the  exact 
profile  plotted  the  grade  line  may  be  drawn  consisting  of  an 
average  line  through  the  profile  representing  a  series  of  grades, 
with  none  exceeding  2  per  cent,  if  possible,  and  with  as  close  a 
balance  between  "cuts"  and  "fills"  as  may  be  secured  in  order 
that  the  haul  for  excavation  and  embankment  may  be  a  mini- 
mum. While  grades  as  high  as  7  or  8  per  cent,  sometimes 
exist  on  interurban  roads  it  will  often  be  found  that  when  the 
first  cost  of  the  extra  heavy  car  equipment  and  possibly  the 


TRACK  LAYOUT  AND  CONSTRUCTION. 


207 


station  equipment  necessary  to  climb  these  grades,  together  with 
the  annual  cost  of  extra  power  required  are  balanced  against  the 
fixed  charges  on  the  extra  cost  of  reducing  the  grade  by  means 
of  a  deeper  cut  or  a  slight  change  of  route,  the  latter  policy  would 
have  been  the  better  of  the  two. 

Before  accurate  estimates  can  be  made  or  contracts  let  for 
preparing  the  sub-grade  it  will  be  necessary  to  learn  something 
more  of  the  character  of  the  sub-soil.  It  will  be  assumed  that 
the  general  nature  of  the  country  and  its  geological  formation  were 
carefully  noted  during  the  preliminary  survey,  since  the  decision 
of  the  proper  route  depends  largely  upon  such  a  study,  especially 
when  a  river  is  to  be  paralleled  and  possibly  bridged  occasionally. 
It  is  now  necessary,  however,  to  have  test  borings  made  as  deep  as 
the  deepest  proposed  cut  at  intervals  along  the  line  sufficiently 
frequent  to  obtain  a  good  idea  of  the  type  of  excavation  to  be 


Uuless  otherwise 
ordered 


Fig.  79. 


expected  and  the  necessity  of  driving  piles  or  installing  mattress 
concrete  or  timber  in  case  of  possible  quick  sand.  A  contract  can 
usually  be  placed  for  such  borings  with  their  results  either  repre- 
sented to  scale  on  a  drawing  for  each  station  or  better  by  a 
glass  tube  filled  to  scale  with  the  various  strata  of  sub-soil  found. 
With  this  information  at  hand  a  series  of  cross  sections  at  right 
angles  with  the  base  line  at  stations  100  or  200  ft.  apart,  or  possibly 
less  where  the  profile  is  very  irregular,  may  be  made  and  the 
volume  of  excavation  and  embankment  calculated.     A  list  of  cut 


2o8  ELECTRIC    RAILWAY   ENGINEERING. 

and  fill  expressed  in  cubic  yards  of  each  type  of  sub-soil  from 
solid  ledge  to  soft  clay  may  then  be  made  for  each  mile  of  road 
and  estimates  readily  calculated  and  contracts  signed.  Typical 
sections  of  cuts  and  embankments  will  be  found  in  Fig.  79,  while 
estimates  of  their  respective  costs  in  the  South  will  be  found  at  the 
end  of  the  chapter.  These  latter  values  vary  greatly  with  local 
conditions  and  are  usually  based  upon  a  certain  maximum  length 
of  haul  between  a  cut  and  the  corresponding  fill  into  which  the 
excavated  material  may  be  deposited. 

Ballast. — It  is  safe  to  say  that  the  experience  of  interurban 
roads  which  have  been  operating  for  some  time  demonstrates  the 
fact  that  money  expended  in  first  class  sub-grade  construction  and 
rock  ballast  proves  to  be  the  most  economical  in  reducing  main- 
tenance charges  and  providing  a  smooth  riding  roadbed  which, 
does  not  quickly  wear  out  both  itself  and  the  rolling  stock. 

The  ballast,  which  is  that  portion  of  the  roadbed  upon  which  the 
ties  are  placed,  should  be  sufiiciently  porous  to  permit  the  water 
to  run  off  freely.  The  best  ballast  is  recognized  to  be  crushed 
rock  capable  of  passing  through  a  i  1/2  in.  ring.  Coarse  gravel, 
however,  makes  a  very  good  substitute  and  is  very  often  used 
because  of  its  lower  cost.  Fortunate  indeed  is  the  road  that 
secures  with  its  right-of-way  one  or  more  borrow  pits  containing 
good  ballast  gravel.  This  ballast  is  laid  for  a  depth  of  6  to  18  in. 
under  the  ties  and  should  cover  the  ties  to  the  base  of  the  rail. 

Ties. — Now  that  the  scarcity  of  good  lumber  is  beginning  to  be 
felt,  with  a  corresponding  increase  in  first  cost,  the  selection  of 
suitable  ties  and  their  treatment  to  insure  long  life  is  becoming 
a  serious  problem.  Pine,  cedar,  white  oak,  red  oak,  fir  and  chest- 
nut are  the  woods  in  most  common  use.  The  choice  between  these 
depends  largely  upon  the  variety  which  is  native  in  the  locality 
in  which  the  road  is  being  built.  Cedar  is  probably  as  long  lived 
as  any,  while  the  ability  of  white  oak  to  hold  spikes  is  probably 
greater  than  any  other  wood.  While  this  variety  of  tie  is  gener- 
ally too  expensive  to  use  throughout,  it  is  often  specified  for 
curves  where  the  strain  on  spikes  is  of  course  greatest. 

Herrick  gives  in  the  following  table  an  approximate  length  of 
life  for  the  different  varieties  of  ties  as  determined  by  Mr.  Hough ^ 

'■  "Practical  Electric  Railway  Handbook,"  by  A.  B.  Herrick. 


TRACK  LAYOUT  AND  CONSTRUCTION.  209 

TABLE  XVIir. 
Life  of  Ties. 

White  oak 7.4  years. 

Red  oak 5.0  years. 

Chestnut 7.1  years. 

Southern  pine 6.5  years. 

White  pine 6.5  years. 

Red  cedar 11. 8  years. 

It  is  generally  considered  advisable  to  specify  preservative 
treatment  for  ties  in  order  to  increase  their  life,  although  it  is 
difficult  to  determine  from  experience  thus  far  just  how  much 
the  life  is  extended  thereby.  Probably  a  fair  average  price  for 
an  untreated  tie  throughout  the  country  is  70  cents  with  a  possible 
15  cents  per  tie  increase  for  treatment.  Ties  which  have  been 
embedded  in  concrete  in  city  construction  have  shown  particularly 
long  life,  averaging  from  10  to  20  years  with  many  rail  replace- 
ments. The  replacement  of  rails  and  removal  and  replacement 
of  spikes  during  realignment  often  shorten  the  life  of  a  tie  when  it 
has  not  decayed.  Screw  spikes  have  been  proposed  to  obviate 
this  difficulty,  but  they  are  little  used  at  present  because  of  their 
higher  first  cost  and  the  greater  time  required  for  installation  and 
removal. 

Reinforced  concrete  and  steel  ties  have  been  experimented 
with,  especially  abroad.  Whereas  concrete  and  steel  substruc- 
tures are  replacing  ties  to  a  large  degree  in  city  streets  the  wooden 
tie  for  interurban  or  steam  railroad  use  has  not  been  replaced  to 
any  extent  in  this  country. 

The  dimensions  of  ties  for  interurban  use  are  similar  to  those 
for  steam  roads,  averaging  6"X8"X8',  although  5-in.  ties  may  be 
found  occasionally.  In  third  rail  construction  a  longer  tie  is 
installed  every  10  ft.  to  act  as  a  support  for  the  third  rail  insulator. 
The  spacing  of  ties  will  be  found  to  vary  from  15  to  30  in.,  but 
an  average  dimension  may  be  taken  as  2  ft.  Ties  which  lie 
under  the  rail  joints  are  placed  nearer  together,  but  their  exact 
spacing  is  dependent  upon  whether  a  suspended  or  supported 
rail  joint  is  used,  as  will  be  described  later. 

One  consideration  in  connection  with  the  selection  of  ties  which 
has  received  very  little  attention  is  the  effect  of  preservative 
treatment  upon  their  resistance.  This  is  of  })articular  value 
J  4 


2IO 


ELECTRIC    R.\ILWAY    ENGINEERING. 


only  where  the  automatic  block  signals  are  installed.  From  the 
discussion  of  the  previous  chapter  it  will  be  seen  that  if  the  resist- 
ance of  the  ties  be  greatly  reduced  they  will  act  as  a  shunt  to  the 
relay  and  possibly  interfere  with  its  proper  operation.  Tests 
recently  made  at  Purdue  University^  upon  the  resistance  of  ties 
recorded  in  the  report  of  the  wood  preservation  committee  of  the 
American  Railway  and  Maintenance  of  Way  Association  prove 


Fig.  8o. 


that  ties  follow  the  laws  of  insulators  in  general,  but  that  when 
treated  with  the  chloride  of  zinc  preservative  process  their  apparent 
resistance  is  lowered.  Calculated  results  based  upon  the  data  of 
these  tests,  assuming  wet  treated  ties  in  wet  ballast,  show  values 
of  resistance  sufficiently  high  to  prevent  serious  interference  with 
signals.  Cases  in  practical  operation  have  been  reported,  how- 
ever, in  which  such  interference  has  been  present. 

Rails. — In  the  selection  of  rails  also,  steam  railroad  practice 
has  been  followed  to  a  great  extent,  although  the  weight  of  rail 
used  is,  on  the  average,  less  with  the  interurban  roads.     This  is 

'  Graduate  Thesis,  Purdue  I'nivcrsity,  by  J.  T.  Butterlield,  1910. 


TRACK  LAYOUT  AND  CONSTRUCTION'. 


211 


possible  because  of  the  lighter  weight  of  trains  and  the  absence  of 
reciprocating  motion.  The  interurban  roads  make  use  of  the 
"T"  rail  almost  exclusively,  averaging  in  weight  from  70  to  80 
lbs.  per  yard.  The  section  which  has  been  very  generally  adopted 
is  the  standard  established  by  the  American  Society  of  Civil 
Engineers  as  shown  in  Fig.  80.  In  city  streets  a  wide  variety  of 
rail  sections  will  be  found  from  the  "T"  rail  to  the  various  shapes 
and  sizes  of  grooved  girder  rails.     The  "T"  rail  has  been  rather 


Fig.  Si. 


generally  objected  to  by  city  authorities  because  of  the  danger 
to  vehicular  traffic  offered  by  the  projecting  head  of  the  rail  and 
the  difficulty  in  paving  close  to  the  rail  with  standard  paving 
blocks.  Two  sizes  of  girder  rails  7  in.  and  9  in.  in  height  respec- 
tively have  come  into  general  use,  the  latter  being  preferred  from 
the  standpoint  of  ease  in  paving.  At  the  igio  annual  convention 
of  the  American  Electric  Railway  Association  the  9  in.  standard 
girder  rail  illustrated  in  Fig.  81  proposed  by  the  Committee  on 
Way  Matters  was  adopted  as  well  as  a  similar  7  in.  section.  These 
are  designed  for  installation  in  city  streets  where  the  traffic  is 
particularly  heavy. 

The    proper   chemical  com{)()sition  of  rails  has  been  a  c|iies- 


212  ELECTRIC    RAILWAY   ENGINEERING. 

tion  under  discussion  for  some  years,  attempts  being  made  to 
obtain  a  hard  rail  which  shall  not  be  so  brittle  as  to  break  readily. 
Low  conductivity  is  also  a  desirable,  although  not  a  governing 
feature.  The  analysis  which  has  been  standardized  by  the 
American  Electric  Railway  Association  is  given  in  the  following 
table : 

TABLE  XIX. 
Standari>  Analysis  for  Steel  ILmls. 


Lower  Desired  Upper 

limit.  composition.  limit. 


Carbon 0.6%                 0.68%  0.75% 

Manganese 0.6%                  0.80%  0.90% 

Silicon  (not  to  exceed) o .  20% 

Phosphorous  (not  to  exceed) j ] ,  o .  04% 


The  above  table  applies  to  open-hearth  steel,  as  the  majority 
of  rails  are  now  being  manufactured  by  the  open-hearth  process. 

The  composition  of  the  third  or  conducting  rail  may  be  such 
as  to  result  in  a  much  softer  and  lower  resistance  rail.  Arm- 
strong gives  the  following  analysis  for  such  rails. 

TABLE  XX. 

^Analysis  for  Third  Rails. 

Carbon  not  to  exceed 0.12  per  cent. 

Manganese  not  to  exceed o. 40  per  cent. 

Sulphur  not  to  exceed o  .05  per  cent. 

Phosphorous  not  to  exceed o .  10  per  cent. 

The  use  of  manganese  steel  for  the  centers  of  special  work  and 
even  for  complete  frogs,  switches  and  curves  has  been  recently 
given  a  great  deal  of  attention  because  of  its  long  life.  While  it 
seems  to  be  the  consensus  of  opinion  among  railway  operators 
that  the  latter  uses  of  manganese  steel  are  only  advisable 
in  extreme  cases  of  heavy  wear,  the  adoption  of  replacable  frog 
and  switch  points  of  this  material  is  very  heartily  sanctioned. 

The  method  of  laying  rails  in  city  streets  departs  greatly  from 

'  Electric  Traction  by  A.  H.  Armstrong. 


TRACK    LAYOUT   AND    CONSTRUCTIOX.  213 

inlcrurban  practice,  a  lil^eral  use  of  concrete,  steel  and  sand  in 
the  sub-grade  being  common  practice.  Rails  are  often  tempo- 
rarily supported  upon  wooden  ties  spaced  5  ft.  or  more  apart  in 
order  to  hold  them  to  gauge  while  concrete  longitudinal  stringers 
are  being  installed  for  the  final  rail  support.  Iron  chairs  embed- 
ded in  the  concrete  serve  to  grip  the  rail  flanges  after  the  concrete 
is  set.  Less  elaborate  installations  involve  the  use  of  the  usual 
number  of  wooden  ties  laid  in  concrete.  This  construction  has 
been  adopted  as  shown  in  Fig.  71  in  Chicago,  where  it  has  been 
the  policy  to  construct  a  permanent  foundation  from  which  the 
rails  may  be  removed  from  time  to  time  and  new  rails  installed. 
This  rigid  construction  of  the  roadbed  is  at  variance  with  the 
method  of  at  least  one  of  the  largest  steam  roads  whose  engineers 
believe  that  the  roadbed  construction  should  be  somewhat 
flexible  in  a  vertical  plane,  being  depressed  slightly  as  the  train 
passes,  but  returning  to  its  original  position  thereafter. 

Rail  Joints. — Aside  from  the  mechanically  rigid  rail  joints 
produced  by  cast  welding,  thermit  welding  and  electric  welding 
discussed  in  some  detail  in  Chapter  VI,  Part  II,  several  other 
types  of  rail  joints  in  rather  more  common  use  should  be  men- 
tioned. The  simplest  and  cheapest  joint  is  of  course  the  four 
or  six  bolt  fish  plate  clamped  on  either  side  of  the  rail  ends.  This 
construction  allows  considerable  vertical  motion  to  the  ends 
of  the  rails  as  the  train  passes  over  them,  causing  the  heads  to  be 
soon  flattened.  The  rail  must  therefore  be  replaced  or  shortened 
because  of  its  worn  condition  at  the  end  before  it  is  seriously 
worn  elsewhere. 

The  other  types  of  joints  most  commonly  used  are  the  Atlas, 
Continuous  and  Weber  joints,  all  of  which  make  use  of  combined 
splice  bars  and  tie  plates  differing  but  slightly  in  design,  i.e.,  they 
all  furnish  an  iron  plate  between  the  foot  of  the  rail  and  the  tie, 
which  plate  is  generally  notched  to  receive  the  spikes  in  order 
to  prevent  creeping.  The  Weber  joint  makes  use  of  a  single 
plate  cast  in  one  piece  with  one  of  the  vertical  plates  while  the 
other  joints  involve  two  half  plates  split  longitudinally  under 
the  center  of  the  rail. 

The  use  of  tie  plates  is  a  matter  open  for  discussion.  They 
probably  increase  the  life  of  the  ties,  especially  when  rather  soft 


214  ELECTIRC    RAILWAY   ENGINEERING. 

wood  is  used,  by  preventing  chafing  between  rail  and  tie,  but 
many  engineers  are  not  convinced  that  this  gain  warrants  the 
extra  expense. 

Rail  joints  may  be  of  the  "suspension"  or  "supported"  type, 
the  former  having  the  rail  ends  between  ties,  while  the  latter 
provides  a  tie  directly  under  the  ends  of  the  rails.  The  former 
seems  to  be  in  more  general  use.  In  case  the  Atlas  rail  joint  be 
selected  the  suspension  type  must  be  used,  as  this  joint  requires 
transverse  bolts  through  the  casting  under  the  rail  flanges  at  the 
end  of  the  rail. 

Both  30  and  60  ft.  rail  lengths  are  in  use,  the  former  being 
preferred  in  interurban  construction  because  of  less  expansion 
troubles  therewith  and  the  greater  ease  of  handling  the  shorter 
length  on  curves.  Where  the  above  features  are  not  objectionable, 
however,  the  60  ft.  rail  has  the  advantage  of  fewer  joints  and 
bonds,  thereby  reducing  slightly  the  first  cost  and  maintenance 
charges. 

Rail  Corrugation. — Quite  recently  a  peculiar  corrugation  of 
the  heads  of  rails,  particularly  near  the  joints,  has  been  reported 
by  many  companies  and  in  many  instances  special  grinding  de- 
vices have  been  designed  to  remove  such  corrugations,  but  in  spite 
of  extended  study  and  discussion  of  the  question  no  satisfactory 
reason  for  the  effect  has  been  found.  It  has  been  variously 
attributed  to  chattering  of  brake  rigging  upon  stopping  the  car, 
the  transverse  nosing  of  trucks,  the  peculiar  chemical  or  mole- 
cular structure  of  the  rails  and  the  possible  formation  of  succes- 
sively soft  and  hard  spots  due  to  some  peculiarity  of  the  rolling 
process.  As  this  effect  has  been  found  under  practically  all 
conditions,  rails  of  one  particular  make  or  in  any  particular  posi- 
tion in  the  roadbed  cannot  alone  be  charged  with  the  difficulty. 

Paving. — The  railway  company  is  usually  required  to  install 
and  maintain  the  pavement  between  tracks  and  for  a  distance  of 
2  ft.  or  more  outside.  If  paving  blocks  are  used  with  anything 
but  a  9  in.  girder  rail  a  special  block  must  be  secured  to  fit  the 
rail  and  provide  a  groove  inside  the  rail  sufficient  to  allow  the 
wheel  flange  to  pass  without  forming  a  dangerous  rut  for  vehicular 
traffic.  Such  grooves  are  rapidly  worn  away  by  the  latter  traffic 
and  the  railway  company  endeavors,  therefore,  so  to  design  the 


TRACK    LAYOUT   AND    CONSTRUCTION. 


215 


track  and  paving  that  the  vehicles  will  not  be  attracted  thereto. 
This  policy  will  often  aid  in  making  schedule  time  in  city  streets 
as  well.  With  the  grooved  girder  rail  the  groove  provides  room 
for  the  flange.  Fig.  71  well  illustrates  paving  construction  with 
this  type  of  rail. 


G&lv.  Through  Bolts 
:  Si"i  2,1-i  I  ^ic'ualv.   W.I.  Washors 
Ralte  'SJ  _  in  34  0  from  lop  of  Bail 


jtor  IIW!  Volls  Use  Sli  I  i'i  U.P.  Cross  Arms 
llh"»  I'-A  i'Top  Louust  Pins 


Fig.  82. 


Overhead  Construction. — Typical  bracket  and  span  overhead 
construction  are  now  so  familiar  to  all,  little  description  is  neces- 
sary aside  from  the  specifications  given  in  Fig.  82  and  8^,  the 
former  representing  the  single  track  bracket  standard  construc- 
tion of  the  Connecticut  Company,  while  the  latter  is  typical  of 
double  track  span  construction  with  two  high  tension  trans- 
mission lines. 

Neither  of  the  abo^•e  illustrations,  however,  shows  the  details 


2l6 


ELECTRIC    RAILWAY    ENGINEERING. 


of  the  trolley  insulation  and  hangers.  It  is  customary  at  pres- 
ent to  use  grooved  hard  drawn  trolley  wire  with  mechanical 
clamps  or  ears  which  spring  into  the  grooves  in  the  wire  and  are 
clamped  therein  by  means  of  four  machine  screws.  Much  time 
is  thus  saved  in  repairs  over  the  old  soldered  ears.  Double 
insulation  is  provided  between  pole  and  trolley  by  means  of  the 
insulating  hanger  and  strain  insulators  in  series.  Strain  insu- 
lators in  span  construction  should  be  sufficiently  near  the  trolley 


Fig.  S- 


so  that  a  broken  "live"  span  cannot  reach  the  ground  and  yet 
sufficiently  far  away  so  that  a  trolley  pole  when  off  the  wire  cannot 
impress  full  potential  upon  the  span  outside  the  strain  insulator. 

Catenary  line  construction,  which  is  meeting  with  favor  even 
for  low  voltages,  was  described  in  a  previous  chapter. 

Lightning  protection  is  provided  for  the  trolleys  and  feeders 
by  mounting  a  low  voltage  lightning  arrester  on  the  pole  top  at 
distances  apart  varying  with  different  companies  from  looo  ft. 
to  several  miles.  Grounds  for  such  arresters  should  be  thor- 
oughly made  by  burying  a  plate  of  copper  or  an  amount  of  scrap 


TR.\CK    LAYOUT   AND    COXSTRUCTIOX.  21 7 

copper  wire  of  large  surface  area  in  coke  in  permanently  moist 
earth  and  connecting  the  arrester  with  this  ground  by  means  of  a 
straight  copper  wire  of  at  least  No.  4  B.  &:  S.  with  well  soldered 
joint  stapled  to  the  pole.  Fairly  good  results  have  been  obtained 
in  new  construction  by  winding  copper  strip  about  the  butt  of 
the  pole  before  installation  and  in  some  cases  with  a  long  pipe 
driven  into  the  ground  containing  a  plug  into  which  the  ground 
wire  is  soldered.  The  practice  of  grounding  lightning  arresters 
to  the  rails  should  be  discontinued  as  it  has  been  found  to  destroy 
the  arresters  without  giving  the  necessary  protection. 

Poles  are  usually  spaced  from  80  to  125  ft.  apart,  the  smaller 
distance  being  used  on  curves.  Poles  should  be  guyed  on  curves 
and  anchors  or  longitudinal  guys  installed  to  support  the  line  at 
least  every  mile.  With  the  present  cost  of  lumber  it  seems  worth 
while  to  treat  the  butts  at  least  with  preservative  compound 
and  often  to  treat  the  entire  pole.  The  poles  should  at  least  be 
kept  well  painted  even  on  interurban  lines.  Iron  poles  have 
found  a  place  in  city  streets  principally  because  of  their  better 
appearance.  Corrosion  can  be  held  in  check  by  painting  fre- 
quently and  by  setting  butts  in  concrete.  In  fact,  the  latter 
method  is  often  used  for  the  protection  of  wooden  poles  even 
after  they  have  begun  to  decay  at  the  surface  of  the  ground. 

Estimates. — Whereas  the  cost  of  materials  varies  so  greatly 
in  different  portions  of  the  country,  estimates  or  actual  costs  of 
construction  must  be  taken  with  a  great  deal  of  caution.  They 
seem  to  be  of  sufficient  value  as  a  study  of  approximate  relative 
values,  however,  to  warrant  listing  herein.  Such  an  estimate 
covering  the  construction  for  an  interurban  line  63  miles  in 
length  in  the  South  will  therefore  be  found  on  page  218. 

The  estimate  represents  an  expenditure  of  $13,700  per  mile  for 
roadbed  and  track  exclusive  of  engineer's  fee  and  contractor's 
profit.  It  is  interesting  to  note  that  of  the  above  total  37.8  per 
cent,  is  labor  and  62.  2  per  cent,  material. 


2l8  ELECTRIC    RAILWAY    ENGINEERING. 

ESTIMATED  COST  OF  ROADBED  CONSTRUCTION. 


Labor. 


Material        Total. 


Clearing  and  Grubbing. 

68  acres  at  $45 

Grading. 

Solid  rock  8000  yds.  at  $0 . 7  5 

Loose  rock  35000  yds.  at  $0.37 

Earth,  7 16000  yds.  at  $0 .  145 

Culverts. 

150  Culverts  varying  from  18"  to  60"  diam. 
Total  4573'. 

Hauling  and  placing 

End  walls  1300  yds.  at  $8 

Timber  bridges. 

41  Pile  bridges,  4752  lin.  ft.  at  $8.80 

I  Frame  bent  bridge,  800  lin.  ft.  at  $10.25.  . 
Steel  Bridges. 

9  Steel  spans  ranging  from  30'  to  130', 
700520  lb.  erect,  at  4  1/8  cents. 

Concrete  piers,  2300  yds.  at  $7.20 

Deck,  2300  yds.  at  $2  .  50 

Track. 

Rail  80  lb.  ;iT,',  8431.7  tons  at  $33.515 

Angle  bars,  21690  prs.  at  .86   

Track  bolts,  86762  at  .04 

Track  spikes,  2010  kegs  at  $5.60 

Bonds,  2 1 160  at  .  60 

Cross  bonds  67  total 

Track  ties,  169860  at  .65 

Switches  compl.,  18  at  $150 

Labor 

Ballast. 

Local  gravel  or  lime  rock 

Fencing  (Wire). 

26900  rds 

Miscellaneous. 

Railroad  crossings  at  $300 

Highway  and  Private  crossings  at  $47 

Signs 


$3,060 

6,000 
,  12,950 
103,820 


995 
10,400 

14,000 
2,73° 

8,280 
675 


$3,060 


122,770 


9,420 


27,8l« 

5.470 


20,815 


5,196 


25.395 

8,280 
1,300 

282,588 

18,653 

3,471 
11,256 

9,500 


so, 018 


47,432 


110,409 
2,700 


26,548 

130,000 

5,380 

200 

1,150 

100 


600 


468,921 


11,112  16,492 

1,000        

4,490       

300  7,240 


Grand  total $866,748 


CHAPTER  II. 
Rolling  Stock. 

Notwithstanding  the  fact  that  electric  traction  has  been  de- 
veloped within  a  comparatively  few  years,  cars  which  are  now 
operated  upon  the  various  city  and  intarurban  lines  of  the  country 
range  from  the  20  ft.  single-truck  made  over  horse-cars  to  the 
60  ft.  magnificent  limited  double-truck  parlor  cars  weighing  from 
40  to  50  tons  and  provided  with  all  the  conveniences  of  the 
Pullman  coach.  With  this  array  of  possible  rolling  stock  to 
choose  from  the  problem  of  car  selection  for  a  proposed  road  or 
for  additions  to  present  equipment  on  city  or  interurban  systems 
is  a  difficult  matter.  Too  little  attention  has  been  given  to  this 
problem  in  the  past,  the  questions  of  sufficient  seating  capacity 
and  finish  often  being  the  principal  considerations  in  the  selection 
of  cars.  These  factors  are  of  course  of  prime  importance,  for  the 
public  patronage  is  not  only  dependent  upon  the  ability  to  obtain 
a  seat  in  a  car,  especially  upon  a  long  journey,  but  also  to  a  sur- 
prising extent  upon  the  appointments  of  the  cars  with  respect  to 
personal  convenience.  That  there  are  several  other  very  im- 
portant factors  to  be  taken  into  account,  however,  will  be  made 
clear  in  the  following  discussion. 

With  the  gradual  increase  in  speed  of  cars  there  came  an 
increasing  number  of  wrecks  which  soon  proved  the  average 
car  construction  to  be  unsuitable  for  withstanding  severe  strains 
and  thereby  protecting  passengers  to  some  extent  from  injury  in 
case  of  collision.  Then  came  a  period  of  marked  increase  in 
the  weight  of  cars  with  correspondingly  increased  capacity  of 
car  ecjuipment  not  only,  but  of  feeders,  and  substation  and  power 
station  capacity  as  well.  Quite  recently,  however,  another 
reaction  has  taken  place,  for  it  has  been  found  that  the  desired 
strength  to  resist  the  abnormal  forces  in  service  may  be  obtained 
by  proper  design  with  even  less  weight.  This  apparently  para- 
doxical condition  is  partly  due  to  the  fact  that  the  use  of  steel  in 

219 


2  20  ELECTRIC    R.\ILWAY    ENGINEERING. 

place  of  wood  will  give  greater  strength  with  less  weight  and  also 
for  the  reason  that  a  car  may  be  considered  as  a  double  truss, 
the  side  frames  acting  as  one  truss  to  transfer  the  load  to  the 
bolsters  and  the  bolsters  in  turn  acting  as  transverse  trusses 
between  the  car  sills  and  the  truck  support.  For  steel  frame 
construction  see  Fig.  84. 

The  desirable  reductions  possible  in  cost  of  power,  car  repairs, 
track  repairs,  fixed  charges  on  power  plant   and    distribution 


Fig.  84. 

system  with  decrease  in  w^eight  of  cars  are  very  clearly  pointed 
out  in  a  paper  by  M.  V.  Ayers,  electrical  engineer  of  the  Boston 
&  Worcester  Street  Railway  before  the  American  Street  and 
Interurban  Railway  Engineering  Association  in  1909.  In  this 
paper  formulae  are  developed  for  the  above  cost  reductions  and 
suggestions  given  for  the  possible  decrease  in  weight  of  cars 
without  a  curtailment  of  strength.  Aside  from  the  above  truss 
design  and  steel  under  framing,  the  use  of  aluminum  and  cast 
bronzes  in  place  of  iron,  soft  woods  in  many  places  instead  of 
hard  w'oods  and  the  reduction  in  the  weights  of  motors  with 
forced  ventilation  are  mentioned. 


ROLLING    STOCK.  221 

Another  very  marked  advance  is  the  standardization  by  the 
above  association  of  the  heights  of  underframes  of  both  inter- 
urban  and  city  cars  and  the  use  of  corrugated  iron  buffers  on  the 
latter  extending  to  the  height  of  the  sills  of  the  former  cars  to 
prevent  telescoping  of  platforms  in  case  of  collision.  Such 
telescoping  was  the  cause  of  much  damage  in  several  recent  and 
very  serious  intcrurban  wrecks  in  the  Middle  West. 

Motor  Equipment. — The  question  of  whether  a  two  or  four 
motor  equipment  should  be  installed  must  be  given  careful  thought. 
Previous  chapters  have  described  the  method  of  determining  the 
total  power  required  for  the  car,  but  whether  this  should  be  sup- 
plied by  two  or  four  motors  is  quite  another  problem.  With 
single  truck  cars  two  motors  only  are  possible.  In  the  case  of 
double  truck  cars  four  motor  equipment  is  probably  most  com- 
monly found,  although  many  roads  are  operating  with  but  one 
motor  per  truck.  Tests  which  have  been  made  with  the  same 
car  equipped  in  both  ways  disclose  the  fact,  which  might  be 
theoretically  predicted,  that  the  four  motor  equipment  will  re- 
quire less  power  for  the  same  schedule.  This  is  largely  due  to 
the  distribution  of  torque  over  the  larger  number  of  driving 
wheels.  This  torque  distribution  as  well  as  the  reserve  capacity 
over  that  called  for  by  the  theoretical  calculations,  especially 
under  the  abnormal  conditions  of  snow  fighting  and  making  up 
lost  time,  are  usually  considered  of  tangible  monetary  value  by 
traction  managers. 

For  these  reasons  the  four  motor  equipment  has  generally 
found  favor.  While  the  control  equipment  and  car  wiring  are 
slightly  more  complicated  wdth  the  four  motor  equipment  the 
ability  to  use  two  motors,  ordinarily  with  one  on  each  truck,  in 
case  of  failure  of  one  or  more  of  the  other  set  is  worthy  of  con- 
sideration. In  short  the  continuity  of  service  and  maintenance 
of  schedule  speed  must  be  thought  of  as  w^ll  as  first  cost  of  equip- 
ment and  operating  expense. 

Trucks. — The  truck  primarily  consists  of  two  pairs  of  wheels 
and  axles  upon  whose  journals  a  steel  framework  is  supported 
by  means  of  combined  spiral  and  elliptical  springs.  This  frame- 
work serves  to  take  the  weight  of  the  car  body  not  only,  but  to 
form  a  support  for  the  brake  rigging  and  a  portion  of  the  weight 


2  22  ELECTRIC    RAILWAY   ENGINEERING. 

of  the  motors  as  well.  Since  the  axles  are  held  in  a  position  par- 
allel to  each  other  by  the  fixed  journal  boxes  the  distance  between 
axles  cannot  exceed  a  certain  value,  generally  7  ft.  6  in.,  because 
of  difficulties  in  following  curves  of  short  radius  in  the  track. 
With  this  limitation  and  with  the  further  fact  demonstrated  by 
practice  that  single  truck  cars  tend  to  rock  badly  in  the  direction 
of  motion,  the  length  of  single  truck  car  bodies  must  necessarily 
be  limited  to  from  22  to  25  ft.  overall.  For  the  longer  cars  two 
trucks  with  king  pins  located  as  near  the  ends  of  the  car  as  pos- 
sible without  interfering  with  vestibule  supports  must  be  used. 

With  either  type  of  truck  the  motors  are  suspended  with  two 
babitted  boxes,  cast  in  one  side  of  the  motor  frame,  bearing  on 
the  car  axle  and  the  opposite  side  of  the  motor  is  hung  by  means 
of  a  flexible  link  from  the  truck  frame.  The  so-called  "nose" 
suspension  provides  but  one  support  between  motor  and  frame, 
while  the  "yoke"  suspension,  as  the  name  implies  furnishes 
two  such  connections.  With  these  suspensions  the  motor 
is  permitted  to  swing  slightly  about  the  car  axle  as  a  center  as 
the  car  passes  over  irregularities  in  the  track,  thus  keeping  the 
pinion  on  the  motor  shaft  at  all  times  in  mesh  with  the  gear  on 
the  car  axle. 

Trucks  are  provided  with  car  wheels  ranging  from  t,^  to  37  in. 
in  diameter,  the  larger  sizes  being  generally  used  in  heavy  inter- 
urban  traction.  Wheels  are  constructed  of  cast  iron  with  chilled 
treads,  cast  steel,  or  a  combination  of  cast  iron  centers  with  steel 
rims.  The  latter  type  has  now  been  largely  replaced  on  inter- 
urban  roads  by  the  cast  steel  wheel,  as  some  difficulties  were 
encountered  due  to  the  steel  rims  working  loose  in  service. 
Wheels  may  be  returned  four  or  five  times  before  scrapping  is 
necessary,  a  reduction  of  from  3/4  to  i  in.  in  diameter  being 
possible  before  wheels  must  be  discarded.  Steel  wheels  will 
range  from  four  to  five  times  the  mileage  of  cast  iron  wheels  and 
the  latter  are  considered  unsafe  above  30  m.  p.  h.  Wheels  vary- 
ing as  much  as  2  in.  in  diameter  have  been  successfully  used  on 
different  axles  of  the  same  car,  although  those  on  the  same  axle 
must  be  of  the  same  diameter.  The  wheels  are  forced  on  the 
axles  under  hydraulic  pressures  of  from  25  to  50  tons,  depending 
upon  the  type  of  wheel  and  size  of  axles. 


ROLLING    STOCK.  223 

Car  axles  arc  turned  from  cold  rolled  steel  and  vary  in  diameter 
from  4  in.  with  the  smallest  motors  up  to  7  in.  with  200  and  250 
h.  p.  motors  in  heavy  service. 

Lubrication  is  ordinarily  provided  to  the  half  bearing  by  means 
of  cotton  waste  soaked  in  grease  with  which  the  journal  box  is 
packed,  although  within  the  last  few  years  an  apparent  saving 
has  been  made  on  some  roads  by  adapting  the  journals  to  oil 
lubrication. 

Trucks  are  provided  with  side  bearing  plates  upon  which 
similar  plates  on  the  under  side  of  the  car  may  rest  when  the 
latter  is  unequally  loaded  or  upon  curves  to  prevent  too  great 
tilting  of  the  car. 

Lighting. — The  very  unsatisfactory  nature  of  car  lighting  at 
the  present  time,  especially  upon  interurban  roads,  has  been 
commented  upon  in  a  previous  chapter.  The  reason  for  this  in 
the  face  of  public  criticism  on  roads  where  everything  else  is  done 
for  the  convenience  and  comfort  of  the  passengers  is  difficult  to 
understand.  The  present  method  of  lighting  is  that  of  using 
several  series  of  five  incandescent  lamps  each  protected  by  fuses 
and  connected  directly  between  the  trolley  and  ground  so  that 
the  lights  will  not  be  extinguished  when  the  circuit  breaker  opens. 
Several  clusters  are  distributed  throughout  the  hood  of  the  car 
and  often  a  light  is  placed  over  each  seat.  The  incandescent 
headlight,  if  one  be  used,  may  be  lighted  in  place  of  the  vestibule 
light  on  the  front  end  of  the  car  by  means  of  a  snap  switch.  All 
the  lights  are,  of  course,  dependent  upon  trolley  voltage  which 
has  been  previously  shown  to  vary  over  a  wide  range  with  more 
than  proportional  variations  in  light  intensity.  A  lighting 
system  independent  of  trolley  voltage  must  sooner  or  later  re- 
place this  unsatisfactory  method  of  car  lighting. 

Arc  headlights  are  generally  used  on  interurban  lines  with 
some  provision  for  operation  upon  city  streets  such  as  a  gauze 
shade,  reduced  voltage,  polarity  reversal  in  the  case  of  the  mag- 
netite arc  or  the  substitution  of  an  incandescent  lamp.  These 
headlights  require  from  4  to  4  1/2  amperes  at  550  volts,  of  which 
over  80  per  cent,  is  wasted  in  external  resistance. 

Heating.  City  cars  and  some  of  the  smaller  inlcrurbanVars 
are  heated  by  means  of  electric  heaters  jjrovided  with  switches 


224 


ELECTRIC    RAILWAY    ENGINEERING. 


located  in  the  vestibule  which  will  permit  several  degrees  of  heat 
by  changes  of  the  heater  coils  from  series  to  parallel  grouping. 
The  problem  of  car  heating,  especially  upon  long  exposed  runs  at 
high  speed  in  the  coldest  weather  is  a  serious  one,  a  car  requiring 
from  lo  to  30  amperes  at  550  volts  for  such  service.  One  large 
city  railway  system  in  particular,  although  able  to  supply  the  de- 
mands of  summer  traffic  with  existing  power  station  equipment 
was  forced  to  install  additional  apparatus  and  enlarge  its  station 
in  order  to  meet  the  car  heating  demand  in  winter. 

Interurban  companies  and  especially  those  operating  single- 
end   cars   have   adopted   the   hot-water   heating  system   almost 


exclusively,  the  heater  being  located  in  one  end  of  the  car,  pref- 
erably in  the  baggage  compartment  or  motorman's  cab.  This 
system  has  the  double  advantage  of  low  cost  of  operation  and 
more  even  distribution  of  heat  in  the  car,  this  being  accomplished 
by  means  of  pipes  encircling  the  car  near  the  floor  as  in  the  case  of 
the  cars  of  steam  railroads. 

Current  Collection. — Little  change  has  been  made  in  the 
overhead  trolley  since  the  earliest  days  of  electric  traction,  its 
operation  being  entirely  satisfactory  except  for  the  very  highest 
speeds  or  for  the  collection  of  very  heavy  currents.  Large  trolley 
wheels  are  used  for  high  speed  service  and  each  road  has  a  par- 
ticular composition  for  the  wheel  casting  which  is  believed  to  be 
best  for  local  conditions.  Wheels  should  run  from  5,000  to 
10,000  miles  before  replacement  is  necessary. 

The  pantograph  bow  collector  is  coming  into  general  use  in 


ROLLING    STOCK. 


225 


high  voltage  high  speed  service.  Such  a  device  is  illustrated 
upon  a  car  in  Fig.  85.  It  is  raised  to  the  wire  by  air  pressure, 
the  controlling  valve  being  in  the  motorman's  cab.  With  this 
type  of  collector  the  alignment  of  the  trolley  wire  is  not  important, 
as  the  collector  is  often  two  or  more  feet  in  length  and  any  trans- 
verse movement  prevents  local  wearing  of  the  collector. 


The  third  rail  shoe  for  collecting  heavy  currents  from  the 
third  rail  mounted  beside  the  running  rails  has  been  referred 
to  previously.  A  view  of  one  of  the  many  types  may  be  found 
in  Fig.  86.  Some  difficulty  has  been  encountered  in  the  past 
with  this  construction  in  winter  for  if  sleet  be  allowed  to  form  on 


2  26  ELECTRIC    RAILWAY    ENGINEERING. 

the  rail  the  shoe  tends  to  ride  on  the  sleet  and  a  poor  contact  with 
much  arcing  results.  Various  methods  have  been  devised  to 
overcome  this  difficulty  with  more  or  less  success.  Those  most 
used  are  a  steel  brush  or  scraper  placed  ahead  of  the  shoe  and 
sprinkling  the  third  rail  with  brine. 

Car  Wiring. — A  great  deal  of  laxity  has  existed  in  the  past  in 
regard  to  car  wiring  and  many  accidents  and  fires  have  resulted 
in  consequence.  As  the  Underwriter's  Code  does  not  rigidly 
apply  since  cars  are  not  insured,  the  tendency  has  been  to  use 
little  care  in  running  the  wires  under  the  car.  Rubber  covered 
wire  is  of  course  used,  but  it  is  customary  to  group  all  the  wires 
together  in  one  or  two  cables  in  a  length  of  canvas  hose  hung 
from  the  car  sills  and  extending  from  motors  to  controllers.  The 
cable  extending  from  the  trolley  base  is  supported  on  the  top  of 
the  car  roof  by  means  of  brass  clips  and  is  carried  either  into  the 
car  vestibule  to  the  circuit  breaker  with  only  the  insulation  of  the 
wire  or,  in  the  case  of  master  control,  it  is  carried  down  one  of 
the  corner  posts  of  the  car  in  moulding. 

Recently  the  Fire  Underwriters  have  drawn  up  a  code  of  rules 
for  car  wiring  and  many  improvements  have  resulted  therefrom. 
Asbestos  lined  conduit  is  now  often  laid  under  the  seats  of  the 
car  for  the  installation  of  cables  while  in  the  best  construction, 
used  especially  in  subway  cars,  iron  conduit  is  installed  as  in 
building  wiring.  Present  practice  also  involves  asbestos  lumber 
or  galvanized  iron  protection  between  wiring  and  wooden  car 
frames,  especially  over  the  rheostats.  Car  wiring  diagrams  will 
be  considered  under  "Types  of  Control,"  Chapter  IV. 

Special  Types  of  Cars. — The  above  discussion  applies  to  all 
types  of  cars.  The  special  features  of  cars  designed  for  a  par- 
ticular service  will  be  outlined  below. 

City  Cars. — In  the  smaller  cities  where  traffic  is  not  particu- 
larly heavy  the  20  ft.  single  truck  car  with  longitudinal  seats  is 
still  used.  The  corresponding  summer  equipment  would  be  a 
20  ft.,  ten  bench  single  truck  car  with  running  board.  Officials 
differ  as  to  the  advisability  of  maintaining  a  double  motor  equip- 
ment and  many  of  the  smaller  roads  shift  the  equipment  twice  a 
year  from  one  type  of  car  to  the  other.  With  single  trucks  this 
involves  considerable  labor,  but  if  double  trucks  be  used  the 


ROLLING    STOCK.  227 

trucks  complete  with  motors  can  be  changed  with  little  trouble. 
Where  summer  traffic  is  heavy,  especially  to  summer  resorts, 
the  35  ft.,  15  bench,  double  truck  open  cars  or  small  trailer  cars 
are  used. 

In  the  large  cities  the  convertible  or  semi-convertible  double 
truck  cars,  Fig.  87,  with  either  transverse  seats  throughout  or  a 
combination  of  transverse  and  longitudinal  seats  are  adopted, 
the  same  cars  being  used  throughout  the  year.  This  avoids 
duplication  of  ef|uipment  and  the  dangers  incident  to  the  opera- 
tion of  the  running  board  type  of  car  in  congested  districts.  Cars 
with    transverse   seats    arc   much    more   comfortable,    especially 


Fig.  87. 


for  long  rides,  but  they  do  not  permit  rapid  ingress  and  egress, 
nor  do  they  provide  the  standing  room  for  a  given  size  of  car 
that  the  longitudinal  seats  furnish.  The  combination  of  both 
types  of  seats  for  long  cars  with  the  section  of  transverse  seats  in 
the  center  of  the  car  permits  the  long-haul  passengers  to  ride  in 
comfort  and  yet  furnishes  more  readily  accessible  seats  and 
standing  room  for  the  local  traffic. 

Pay  as  You  Enter  Cars. — This  type  of  car  which  has  been 
([uitc  recently  adoj)ted  in  the  large  cities  with  considerable  suc- 
cess has  the  advantage  that  the  conductor  may  always  remain  on 
the  rear  platform  to  start  and  stop  the  car  promptly  and  to  avoid 
possible  accidents.  The  probability  of  obtaining  all  the  fares 
when  traffic  is  heavy  is  also  increased.     An  apparent  disadvan- 


228 


ELECTRIC   RAILWAY   ENGINEERING. 


tage  is  the  increased  length  of  stop,  but  this  has  not  proved  to  be 
serious  as  the  platforms  in  this  type  of  car  are  very  large  and 
when  this  platform  is  filled  the  car  is  started.     The  fares  are 


Sigu/'Pleaw  psy  as  you  g:t  on 


Fig 


Fig.  89. 


paid  before  the  passengers  enter  the  car,  but  during  the  period 
the  car  is  in  motion.  This  procedure,  together  with  the  time 
saved  by  the  conductor  being  in  a  position  to  start  the  car 
promptly  has  permitted  the  same  schedule  to  be  maintained  in 


ROLLING    STOCK. 


'.2(J 


several  cities  with  less  cars  where  this  type  of  car  has  been 
adopted.  A  plan  view  of  this  type  of  car  will  be  found  in  Fig. 
88,  while  the  method  of  paying  fare  is  well  illustrated  in  Fig.  89. 
These  cars  are  almost  invariably  designed  for  single  end  operation. 
Suburban  Cars. — This  service  in  large  cities  is  maintained 
with  the  semi-convertible  car  of  the  double  truck  type,  in  some 


Fig.  yo. 

instances  with  the  addition  of  vestibule  doors  operated  by  com- 
pressed air  controlled  by  the  motorman.  With  this  equipment, 
the  motorman  is  required  to  close  all  the  doors  of  the  car  after 
the  starting  signal  has  been  given,  but  before  the  car  is  started. 
In  most  installations  of  this  type  of  car  the  car  step  is  hinged  and 
so  connected  with  the  doors  that  it  is  folded  up  as  the  door  closes. 
This  successfully  prevents  attempts  to  board  cars  when  in  motion. 


Fig.  f)i. 


Open  running  board  cars  are  used  much  more  in  the  East 
than  in  the  Middle  West  for  suburban  service.  Such  a  car  42  ft. 
6  in.  in  length  and  weighing  13  tons  without  electrical  e(|uipmcnt 
is  shown  in  Fig.  90. 

Interurban  Cars. — Cars  which  have  been  developed  for 
interurban  service  which  has  recently  grown  so  rapidl}'.  particu- 


2^0 


ELECTRIC    RAILWAY    ENGINEERING. 


larly  in  the  Middle  West,  are  patterned  after  the  steam  railroad 
coaches  and  often  reach  lengths  of  68  ft.  and  weights  of  50  tons. 
These  cars  are  equipped  with  transverse  seats  and  are  divided 
into  four  compartments,  for  motorman's  cab,  baggage,  smoking 
and  main  passenger  service  respectively.  This  design  of  course 
precludes  double  end  operation.  A  plan  view  of  such  a  car  may 
be  seen  in  Fig.  gi,  while  a  similar  car  designed  as  a  sleeper  and 


-52-0 — ; OTBr-Bumiers 


jJ||LLJi|iiillllLj  LMLJ  Uifev^ 


Jin  IIm 


Fig.  92. 

operated  upon  the  Illinois  Traction  Company's  lines  between 
St.  Louis  and  Peoria,  Illinois,  is  illustrated  in  the  plan  view  of 
Fig.  92. 

Elevated  and  Subway  Cars. — In  the  elevated  and  subway 
service  in  the  largest  cities  a  slightly  different  type  of  car  is  re- 
quired, although  it  is  patterned  closely  after  the  interurban  car. 
Exits  are  so  located  as  to  be  flush  with  the  platform  floors,  no 


Fig. 


steps  being  necessary.  In  Boston  and  New  York  both  side  and 
end  doors  are  provided  and  with  the  traveling  public  trained  to 
enter  by  the  end  door  and  leave  the  car  by  the  side  door,  some 
time  is  gained  at  the  station.  Both  transverse  and  longitudinal 
seats  are  provided.  These  cars  are  designed  to  operate  in  trains, 
each  train  consisting  of  both  motor  cars  and  trailers,  all  motor  cars 
being  operated  by  means  of  the  multiple-unit  control  from  the 


ROLLING    STOCK.  23 1 

motorman's  cab  of  the  forward  car.  In  the  New  York  subway 
steel  cars  are  now  being  adopted,  one  of  this  type  being  ilkis- 
trated  in  Fig.  93. 

While  the  life  of  cars  will  vary  from  ten  to  twenty  years,  de- 
pending upon  the  type,  severity  of  service  and  the  attention 
which  they  receive  in  the  shops,  obsolescence  has  been  the  reason 
for  discarding  most  of  the  cars  used  thus  far,  i.e.,  trafl&c  demand 
has  required  that  larger  and  better  cars  replace  those  in  operation 
before  the  latter  were  actually  worn  out. 


CHAPTER  III. 
Motors. 

Much  of  the  theory  underlying  the  operation  of  the  direct 
current  series  motor  has  been  discussed  in  a  previous  chapter. 
A  brief  outline  of  their  construction  and  selection  together  with 
the  principle  of  operation  of  the  alternating  current  motors  used 
in  railway  systems  will  be  herein  considered. 

Direct  Current  Motor. — The  direct  current  series  railway 
motor,  Fig.  94,  differs  from  the  stationary  type  principally  in  the 
design  of  the  frame,  that  of  the  former  motor  consisting  of  a  box- 
like iron  casting  split  in  a  plane  through  the  center  of  the  shaft 


Fig.  94. 

and  hinged  in  such  a  manner  that  the  lower  half  of  the  frame 
with  two  field  poles  and  windings  may  be  lowered  for  inspection 
of  the  armature  with  the  motor  in  place  on  the  truck.  The  larger 
motors  are  of  the  so-called  "box"  type  with  the  frame  in  a  single 
casting.  The  armature  is  removed  from  this  motor  by  taking  off 
the  end  bearing  plate  and  drawing  the  armature  out  in  a  direction 
parallel  with  the  shaft  through  the  opening  thus  made.  The 
motor  must  be  removed  from  the  truck  for  this  operation.  The 
frames  of  both  types  of  motors  are  provided  with  openings  and 

232 


MOTORS  233 

moisture-proof  cover  plates  for  ready  access  to  armature,  com- 
mutator and  connecting  cables.  These  cables  are  brought  out 
through  insulating  bushings  in  the  frame  of  the  motor,  which  are 
usually  located  on  the  side  next  to  the  truck  bolster,  in  order  that 
the  movement  of  these  cables  may  be  least  when  rounding  curves. 

Railway  motors  are  generally  of  the  four  pole  type  with  the 
axes  of  the  poles  at  an  angle  of  45°  with  the  horizontal  in  the  split 
frame  types.  Field  coils  are  wound  with  rubber  or  asbestos 
covered  wire  with  asbestos  insulation  between  layers  or  in  the 
larger  motors  with  copper  strip.  The  coils  are  taped,  impreg- 
nated with  insulating  compound  with  the  vacuum  process  and 
waterproofed. 

Two  sets  of  bearings  are  provided  in  the  frame,  one  pair  for  the 
car  axles  and  the  second  for  the  armature  shaft.  These  are 
of  babbit  lined  cast  bronze. 

The  armature  and  commutator  are  not  unlike  those  of  station- 
ary motors  except  that  the  armature  is  series  wound  and  requires 
but  two  sets  of  brushes.  These  are  placed  on  the  top  portion 
of  the  commutator  and  are  therefore  accessible  through  trap 
doors  in  the  floor  of  the  car.  The  brush  holders  are  fixed  in 
position  and  support  the  carbon  brushes  in  a  radial  position  on 
the  commutator  so  that  the  motor  may  operate  equally  well  in 
either  direction. 

Coniniutating  Pole  Motors. — As  in  the  case  of  direct  current 
stationary  motors  and  generators,  the  rather  marked  advantages 
of  the  commutating  pole  are  applied  to  the  railway  motor.  These 
commutating  poles  are  auxiliary  poles  provided  with  a  winding 
connected  in  series  with  the  armature.  As  the  magnetic  flux 
in  these  poles  will  vary  with  the  armature  current  the  serious 
effects  of  armature  reaction  upon  commutation  are  neutralized 
at  all  loads  by  the  flux  from  these  auxiliary  poles.  The  latter 
are  so  designed  and  located  that  the  short  circuit  current  in  the 
coil  under  the  brush  is  small  and  sparking  at  the  brushes  there- 
fore a  minimum.  As  the  output  of  the  motor  is  often  limited  by 
commutation  as  well  as  temperature  rise,  the  overload  capacity 
will  be  increased  and  its  maintenance  cost  reduced.  It  is 
claimed  that  100  per  cent,  overload  may  be  suddenly  thrown  on 
and  off  such  a  motor  without  sparking  at  the  brushes. 


234  ELECTRIC    RAILWAY    ENGINEERING. 

Single  Phase  Motors. — With  the  increase  in  length  of  inter- 
urban  lines  and  their  large  power  demands  together  with  the 
realization  of  the  high  first  cost  and  maintenance  charges  on  the 
converting  equipment  necessary  for  long  direct  current  roads, 
came  the  serious  study  of  the  possibilities  of  alternating  current 
motors  for  railway  use.  It  was  at  once  recognized  that  if  a 
satisfactory  alternating  current  railway  motor  could  be  developed 
considerable  saving  could  be  made  in  the  above  factors  and  a 
marked  simplification  in  the  distribution  system  effected,  as 
pointed  out  in  the  chapter  on  the  distribution  system,  to  say 
nothing  of  the  possible  reduction  in  distribution  system  losses 
due  to  the  increase  in  trolley  voltage.  As  the  polyphase  motors 
which  have  been  developed  were  of  the  constant  speed  type 
with  inherent  characteristics  unfavorable  for  traction  and  since 
the  advantages  of  polyphase  transmission  at  high  voltage  can 
be  gained  without  the  complication  of  a  polyphase  distribution 
system  and  car  circuits,  the  attention  of  American  engineers  was 
first  turned  to  the  development  of  the  single-phase  motor  for 
traction  purposes. 

This  development  may  be  approached  either  by  endeavoring 
to  adapt  the  direct  current  series  motor,  whose  characteristics 
have  proved  satisfactory  for  traction  purposes,  for  use  upon 
single-phase  alternating  current  circuits  or  the  alternating  current 
induction  motor  may  be  studied  with  a  view  toward  redesigning  it 
for  railway  use.  Both  of  these  viewpoints  will  be  considered  in 
the  order  mentioned. 

Adaptation  of  the  Direct  Current  Series  Motor. — Those 
familiar  with  the  direct  current  motor  w^ill  remember  that  a 
reversal  of  the  current  in  either  armature  or  field  alone  will 
reverse  the  direction  of  rotation  of  the  motor,  whereas  a  reversal 
of  both  field  and  armature  connections  will  not  change  its  direc- 
tion of  rotation.  It  might  be  predicted  therefore  that  when  a 
direct  current  series  motor  is  connected  to  an  alternating  current 
circuit  of  proper  voltage,  the  motor  would  operate.'  This  was 
found  to  be  the  case,  although  many  eiTects  of  the  alternating 
current,  which  are  discussed  below,  cause  the  motor  to  operate 
unsatisfactorily  from  a  practical  standpoint  unless  several  changes 
are  made  in  its  design. 


MOTORS. 


235 


The  e.  m.  f.  impressed  upon  a  direct  current  series  motor  is 
balanced  by  the  sum  of  counter  e.  m.  f.  of  revolution  (Ej  and  the 
(IR)  fall  of  potential  in  field  and  armature  windings.  In  addition 
to  these  there  exists  in  the  series  motor  operating  upon  an  alter- 
nating current  circuit  the  reactive  voltage  of  the  series  field  and 
armature  vi^indings. 

The  reactive  voltages  are  due  to  the  self  Induction  of  the  re- 
spective windings  or  better  to  the  cutting  of  the  conductors  by 
the  lines  of  leakage  magnetic  force  which  encircle  one  set  of  con- 
ductors onlv  and  are  therefore  not  useful  in  producing  counter  or 


Fig.  (;5. 

energy  electromotive  force.  This  voltage  is  90°  in  advance  of 
the  current  and  may  be  treated  as  though  there  were  an  external 
choke  coil  of  corresponding  reactance  connected  in  series  with 
the  motor.  It  is  directlv  proportional  to  the  frequency  of  the 
voltage  sypply. 

With  these  voltages  in  mind  the  vector  diagram  of  the  motor 
may  be  drawn  as  in  Fig.  95  where 

E     =  Impressed  voltage. 
E,   =  Counter  e.  m.  f.  of  revolution. 
I      =  Current  in  armature  and  field. 
R^  ==  Resistance  of  armature. 
X^  =  Reactance  of  armature. 
Rf   =  Resistance  of  field. 
Xf  =  Reactance  of  field. 
9^   =  Angle  between    impressed    voltage    and    current 
whose  cosine  is  the  power  factor  of  the  motor. 


236 


ELECTRIC    RAILWAY   ENGINEERING. 


From  the  diagram  it  will  be  seen  that  any  change  of  design 
that  will  reduce  (Xf)  and  (XJ  will  increase  the  power  factor  of 
the  motor.  This  is  a  desirable  change  as  a  higher  power  factor 
results  in  smaller  losses  and  higher  torque  in  the  motor  not  only, 
but  either  lower  losses  or  less  copper  in  the  distribution  system 
as  well.  The  reactance  voltage  of  the  armature  (IX J  may  be 
more  or  less  completely  neutralized  by  means  of  a  compensating 
winding  which  will  be  subsequently  explained,  while  that  of  the 
field  can  only  be  reduced  by  reducing  the  turns  on  the  field  or 
the  magnetic  induction. 

Before  these  possible  changes  are  studied  further  the  question 
of  commutation  may  well  be  investigated,  for    the    commuta- 


FlG.    96. 

tion  of  a  direct  current  motor  operating  upon  alternating  current 
is  noticeably  poor.  It  will  be  remembered  that  in  the  commu- 
tation of  direct  current  motors,  care  must  be  taken  to  have  the 
current  a  minimum  in  the  coil  or  coils  which  are  short  circuited 
by  the  brushes  in  order  that  the  spark  which  occurs  when  the 
coil  is  disconnected  from  the  brush  by  the  movement  of  the  com- 
mutator may  not  be  serious.  Reference  to  Fig.  96  will  show, 
however,  that  there  is  an  additional  factor  to  be  considered  in  the 
commutation  of  an  alternating  current  motor.  The  motor  is 
Cj[uite  similar  to  a  transforrner  in  that  it  has  a  magnetic  circuit 
surrounded  by  two  sets  of  coils,  the  field  and  the  armature.  The 
pulsating  flux  set  up  by  the  field  generates  an  electromotive  force 
due  to  this  transformer  action  in  the  coils  of  the  armature,  those 
coils  in  the  plane  (a'b')  which  enclose  the  greatest  number  of 


MOTORS.  237 

magnetic  lines  of  force  generating  the  highest  voltage  and  those 
in  the  plane  (ab)  theoretically  zero  voltage.  But  one  or  more 
of  the  coils  in  plane  (a'b')  are  short  circuited  by  the  brushes. 
A  large  current  flows  through  this  coil  therefore  as  in  the  case  of 
a  short  circuited  secondary  coil  on  a  transformer.  Unless  the 
design  is  altered  so  as  to  reduce  this  current,  vicious  sparking  will 
take  place  and  seriously  limit  the  commutating  capacity  of  the 
motor. 

Two  methods  of  reducing  this  short  circuit  current  are  in 
general  use.  One  makes  use  of  an  auxiliary  coil  placed  90  elec- 
trical degrees  from  the  field  coils  as  in  the  case  of  the  commutating 
poles  on  direct  current  motors.  This  so-called  "compensating" 
coil  is  in  series  with  the  armature  and  is  designed  of  such  strength 
as  to  neutralize  the  combined  effect  of  transformer  e.  m.  f.  and 
armature  reactance  e.  m.  f.  While  such  a  coil  can  be  made  to 
perform  such  neutralization  for  one  load  and  partially  neu- 
tralize the  e.  m.  f.  on  all  loads,  its  effect  is  not  complete  over  the 
entire  range  of  load,  it  being  particularly  faulty  at  very  light  loads. 
One  of  the  large  manufacturing  companies  overcomes  this  light 
load  fault  by  inserting  "preventive"  leads  between  the  point 
where  connection  is  made  between  armature  coils  and  the  com- 
mutator. These  leads  are  of  relatively  high  resistance  and 
therefore  tend  to  limit  the  short  circuit  current  to  a  minimum. 
As  the  current  circulating  through  the  armature  coils  encounters 
the  resistance  of  the  preventive  leads  only  as  it  flows  into  or  out 
from  a  brush,  the  heat  loss  in  the  leads  is  not  large.  The  com- 
bination of  compensating  cofls  and  preventive  leads  not  only 
puts  the  commutation  of  the  alternating  current  series  motor  on 
a  par  with  that  of  the  diiect  current  motor,  but  it  increases  the 
power  factor  to  a  practical  operative  value  as  well. 

Returning  to  the  question  of  reducing  the  reactance  e.  m.  f. 
of  the  field  in  order  that  the  power  factor  may  be  still  further 
increased.  If  this  be  done  by  reducing  the  field  flux,  the  capacity 
of  the  motor  is  correspondingly  lowered.  It  is  actually  accom- 
plished in  practice,  therefore,  by  reducing  the  number  of  field 
turns  to  from  20  to  25  per  cent,  of  those  in  a  direct  current  motor 
of  similar  characteristics.  This  is  rather  diflicult  with  the  large 
capacity  motors  having  a  relatively  large  number  of  poles. 


238  ELECTRIC    RAILWAY    ENGINEERING. 

Aside  from  the  above  changes  in  design  which  are  necessary 
in  order  to  adapt  the  direct  current  motor  to  use  with  alternating 
current,  the  field  must  be  laminated  as  well  as  the  armature  to 
prevent  serious  eddy  current  losses.  The  reluctance  of  the 
magnetic  circuit  must  be  reduced  in  order  that  the  flux  may  not 
be  sacrificed  with  a  smaller  number  of  field  turns  and  joints  are 
therefore  eliminated  and  the  sectional  area  of  the  poles  increased. 
Theoretically  the  length  of  the  air  gap  might  be  shortened  to 
produce  the  desired  reduction  in  reluctance,  but  this  is  not  con- 
sidered advisable  from  a  practical  operating  standpoint,  for  with 
the  direct  current  motors  the  bearings  often  wear  to  such  an  ex- 
tent that  the  armature  rubs  on  the  lower  field  poles. 

Adaptation  of  Induction  Motor. — The  evolution  of  the  single 
phase  induction  motor  into  the  alternating  current  series  railway 
motor  has  been  very  clearly  explained  from  the  theoretical  stand- 
point by  McAllister.^  Briefly  the  development  is  as  follows: 
Suppose  a  single-phase  induction  motor  stator  to  be  provided 
with  an  armature  similar  to  that  of  a  direct  current  series  motor 
and  the  stator  and  armature  windings  to  be  connected  in  series. 
McAllister  shows  very  clearly  that  with  all  possible  ratios  of  field 
to  armature  turns  the  power  factor  wfll  not  exceed  45  per  cent. 
and  the  maximum  limit  of  the  ratio  of  starting  to  synchronous 
torque  wfll  be  in  the  neighborhood  of  125  per  cent.  Both  of  these 
values  are  too  small  for  a  satisfactory  railway  motor. 

If  the  reluctance  of  the  air  gap  between  polar  regions  be  in- 
creased by  forming  polar  projections  in  the  stator  fields  such  that 
the  ratio  of  reluctance  of  the  leakage  path  between  poles  to  that 
under  the  poles  may  be  considered  as  infinite,  the  power  factor 
and  torque  ratio  may  be  increased  over  a  wide  range  by  properly 
proportioning  the  armature  and  field  turns.  The  successful 
railway  motor  may  be  considered,  therefore,  as  an  induction 
motor  stator  with  projecting  poles  enclosing  an  armature  similar 
in  design  to  that  of  a  direct  current  series  motor. 

Construction  of  the  Single-phase  Motor.— As  the  result  of 
the  above  studies  a  motor  has  been  developed  which  is  giving 
very  satisfactory  results  upon  single-phase  railway  systems  of 

'  Alternating  Current  Motors  by  McAllister. 


MOTORS. 


239 


low  frequency  (25  cycles)  especiall}'  in  the  larger  sizes  which  have 
been  applied  to  locomotives. 

Such  a  motor,  Fig.  97,  does  not  appear  materially  different 
from  the  direct  current  motor,  consisting  of  a  cast  steel  box  type 
frame  supporting  the  laminated  iron  stator  which  is  so  punched 
as  to  form  polar  projections.  These  are,  however,  shorter  than 
in  the  direct  current  motor.  The  motors  are  provided  with  four 
or  six  poles  and  their  field  windings  are  of  the  distributed  type 
similar  to  those  of  the  single-phase  induction  motor.     The  wind- 


Fio.  97. 


ing  is  of  heavy  strap  copper,  however,  and  consists  of  a  relativelv 
few  turns.  Between  the  main  field  windings  are  located  the 
compensating  windings  connected  in  series  with  the  armature. 
The  armature  is  practically  identical  with  that  of  the  direct  cur- 
rent motor  with  the  exception  that  because  of  the  lower  voltage 
and  consequently  higher  current  for  which  it  is  designed  it  is 
usually  necessary  to  provide  one  set  of  brushes  for  each  pole. 

Characteristics. — The  characteristics  of  the  single-phase 
motor  are  strikinglv  similar  to  those  of  its  competitor,  as  will  be 
seen  by  comparing  Figs.  98  and  13.  The  efficiency  of  the  former 
motor  is  slightly  lower  and  the  torque-current  curve  slightly  more 


24© 


ELECTRIC   RAILWAY  ENGINEERING. 


concave  owing  to  the  lower  induction  for  which  the  alternating 
current  motor  is  designed.  With  the  fields  unsaturated,  therefore, 
the  torque  will  vary  with  the  square  of  the  current. 

Operation  on  Direct  Current. — One  of  the  most  important 
features  to  commend  the  single-phase  series  motor  as  above 
described  is  its  satisfactory  operation  on  direct  current  circuits. 
If  the  changes  which  have  been  made  to  adapt  the  motor  to  alter- 


GO 


50 


iO 


30 


30 


10 


CHARACTERISTIC  CURVES 

OF  125  H.P.  SINGLE  PHASE 

25  CYCLE  A.C.  MOTOR        ,, 
DIAMETER  OF  WHEELS  371/2 
GEAR  RATIO   2.33 

"J 

5  s 

5 

\ 

24U0 

? 

\ 

/ 

(2 

100 
90 

N 

/ 

/ 

2000 

\ 

Ponder  j 

^Ct( 

&■•     . 

/ 

Met 

^f 

riciencv. 

>J 

z 

80 
70 
CO 

50 

\ 

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1600 

^». 

^ 

1200 

\ 

^ 

b 

4 

800 

/ 

C> 

r 

400 

y 

^ 

100 


200 


300     400 
Amperes 

Fig.  98. 


500 


700 


nating  current  are  reviewed  it  will  be  noted  that  no  change  made 
impairs  its  use  with  direct  current.  Since  it  is  highly  important 
that  interurban  roads  operate  their  cars  to  the  center  of  the  termi- 
nal cities  over  the  existing  direct  current  trolley,  this  feature  of  the 
series  alternating  current  motor  is  of  greatest  value.  Whereas 
the  control  system  must  be  duplicated  to  some  extent,  as  will 
be  seen  in  the  next  chapter,  the  flexibility  of  operation  is  well 
worthy  of  the  slightly  added  complication. 


MOTORS. 


241 


Repulsion  Motor.' — When  it  was  found  that  a  corrective 
current  could  be  made  to  flow  in  the  armature  of  an  alternating 
current  armature  by  means  of  induction  between  windings  as  in 
the  case  of  the  transformer,  it  was  inferred  that  such  a  current 
might  be  made  to  produce  a  torque  without  connection  between 
armature  and  iield  as  in  Fig.  99.     Such  a  motor  was  found  to 


Series  Field 


CoiupcnsatiK!^ 
Field 


P"iG.   99. 

operate  satisfactorily,  the  brushes  being  short  circuited  to  allow 
the  torque  producing  currents  to  flow  in  the  armature  windings. 
The  characteristics  of  such  a  motor  are  similar  to  those  of  the 
series  motor.  This  motor  has  been  designated  as  the  repulsion 
motor.  Although  it  was  expected  that  it  would  find  a  ready  ap- 
plication in  the  railway  field  it  has  not  come  into  use  largely 
because  of  its  inability  to  operate  upon  direct  current  systems 
and  the  additional  fact  that  it  apparently  has  no  marked 
advantages  over  the  series  motor. 

■The  Alternating  Current  Railway  Motor  by  C.  P.  Steinmetz,  A.  I.  E.  E.,  \'oI. 
XXIII. 

Speed  Torque  Characteristics  of  the  Single-phase  Repulsion  ]Motor  b)-  ^^'alter 
I.  Slichter,  A.  I.  E.  E.,  Vol.  XXIII. 

Alternating  Current  Motors  by  McAllister. 
16 


242  ELECTRIC    JL-^ILWAY   ENGINEERING. 

Induction  Motor. — The  induction  motor  has  characteristics 
similar  to  those  of  the  shunt  direct  current  motor  and  is,  therefore, 
generally  unfit  for  railway  service.  It  may  be  designed,  however, 
for  several  different  speeds,  usually  by  placing  a  winding  upon 
the  rotor  and  varying  the  resistance  in  the  rotor  circuit  or  in  some 
cases  by  the  so-called  concatenation  method  in  which  the  stator 
of  one  motor  is  supplied  from  the  rotor  circuit  of  a  second  motor. 
With  these  adaptations  this  motor  has  been  considerably  used 
abroad  for  railway  service  and  in  one  installation  in  this  country, 
upon  the  Great  Northern  Railway^  where  the  requirements  seemed 
to  be  particularly  well  filled  by  a  motor  of  constant  speed  charac- 
teristics. 

Frequency. — The  question  of  frequency  has  not  been  directly 
referred  to  in  the  above  discussion.  If  reference  be  made  again 
to  the  factors  which  were  necessarily  changed  in  the  direct  current 
motor  to  adapt  it  to  alternating  current  operation  it  will  be  noted 
that  these  factors,  principally  reactance  voltages,  are  reduced  by 
reduced  frequency.  The  lower  the  frequency,  therefore,  the 
easier  it  becomes  to  design  a  satisfactory  alternating  current  rail- 
way motor  and  the  greater  the  capacity  which  it  is  possible  to 
obtain  with  a  given  size  and  weight  of  frame  and,  therefore,  the 
greater  the  capacity  that  can  be  supplied  to  a  single  truck  or  to  a 
single  pair  of  driving  wheels. 

Rating. — Railway  motors,  because  of  their  rather  intermittent 
service  at  varying  loads  with  a  greater  amount  of  ventilation  in 
actual  use  than  upon  the  testing  floor,  are  rated  differently  than 
other  electrical  machinery. 

A  motor  is  said  to  be  of  a  certain  capacity  expressed  in  horse 
power  if  it  will  delvelop  such  a  horse  power  continuously  for  i  hr. 
with  a  temperature  rise  of  75°  C.  above  the  room  temperature 
corrected  to  25°  C.  when  operating  with  the  openings  in  the  motor 
frame  uncovered.  This  represents  a  rather  arbitrary  rating,  but 
offers  a  basis  for  the  comparison  of  motors. 

Motor  Selection.— The  method  of  determining  the  total  power 
required  to  operate  the  car  has  been  explained  in  a  previous 
chapter.     After  the  number  of  motors  per  car  has  been  decided 

'  The  Electric  Svstem  of  the  Great  Northern  Railway  Company  at  Cascade 
Tunnel  by  Car>'  T.  Hutchinson,  A.  I.  E.  E.,  Vol.  XXVIII. 


MOTORS.  243 

upon  as  outlined  in  the  last  chapter,  the  capacity  of  the  motors 
to  be  installed  may  be  approximately  determined  by  dividing  the 
average  car  demand  expressed  in  horse  power  for  the  various 
runs  by  the  number  of  motors  per  car.  If  care  be  taken  not  to 
load  the  motor  continuously  with  its  rated  load  and  still  make 
due  allowance  for  its  overload  capacity  for  short  intervals  and 
the  extra  demands  of  abnormal  service,  this  method  should  per- 
mit a  correct  selection  of  the  nearest  standard  motor  to  be  made. 

Several  other  methods  of  making  this  selection  may  be  adopted, 
however,  and  it  is  always  well  to  check  the  motor  capacity  chosen 
by  two  or  more  processes.  They  will  be  briefly  explained  in 
order  of  their  ease  of  application. 

Selection  by  Comparison. — A  very  rough  and  simpie  method 
quite  commonly  used  is  to  prepare  a  table  from  technical  jour- 
nals or  the  railway  census  of  the  equipments  of  various  roads 
operating  under  as  nearly  as  possible  the  same  conditions  as  the 
proposed  road.  This  table  should  include  number  and  capacity 
of  motors,  average  voltage,  schedule  speed,  weight  of  cars,  lay- 
over at  terminals,  stops  per  mile,  average  grade  and  if  possible 
the  watt  hours  per  ton  mile  demanded.  By  comparison  with  such 
a  table  the  correct  standard  size  of  motor  for  the  new  equipment 
may  readily  be  determined. 

Effective  Current  Method. — It  is  possible  to  obtain  from 
manufact-urers'  test  records  not  only  the  rating  of  the  motor,  but 
also  its  continuous  current  capacity  at  one  or  more  average  vol- 
tages, i.e.,  the  current  which  may  be  supplied  to  the  motor  con- 
tinuously without  exceeding  the  limit  of  75°  C.  temperature  rise. 
The  temperature  curves  of  Fig.  13  may  also  be  obtained  from 
which  the  time  required  to  rise  to  75°  C.  above  the  room  tempera- 
ture from  the  start  with  the  motor  cold  can  be  found  for  each 
value  of  current  supplied  to  the  motor,  as  well  as  the  time  recjuircd 
to  rise  2d°  above  75°  C.  for  the  various  possible  over-load  currents. 
In  making  use  of  these  data  it  should  be  remembered  that  the 
heating  of  a  motor  is  proportional  to  the  square  of  the  current. 
The  heating  value  of  the  current  or  "eiTective"  current  for  a 
given  run  is  not  the  average  ordinate  of  the  current-time  curve 
of  that  run,  but  the  square  root  of  the  average  squared  current. 
If  then  the  effective  current  for  the  various  runs  as  determined 


244 


ELECTRIC    R.\ILWAY   ENGINEERING. 


from  the  current-time  curves  be  compared  with  the  continuous 
current  rating  of  the  motors  with  due  allowance  for  temperature 
rise  of  short  duration  produced  by  overload  currents  as  deter- 
mined from  the  temperature  curve,  the  proper  motor  may  be 
readily  selected.  In  short,  a  temperature  time  curve  is  really 
determined  for  the  various  runs  and  the  motor  so  selected  that 
this  curve  will  not  exceed  75°  C.  rise  for  other  than  short  inter- 
vals of  time. 


0     20 


40       60       m      100      l:iO     140     160     180     300 
Commercial  Rating  of  Motor  in  H.P. 


Fig.  ioo. 

Method  Proposed  by  Armstrong. — In  a  paper  before  the 
American  Institute  of  Electrical  Engineers^  Armstrong  suggests 
that  a  series  of  curves  such  as  Fig.  loo,  each  representing  the 
motor  capacity  required  for  a  given  weight  of  car  per  motor  and 
for  a  certain  speed,  acceleration,  etc.,  be  prepared  from  theoret- 
ical and  practical  test  data  and  used  for  quick  approximations 
of  motor  capacity.  Fig.  loo  is  plotted  for  straight  level  track 
with  the  following  assumed  values: 

Gross  accelerating  force,  120  lbs.,  per  ton. 

Braking  decelerating  force,  120  lbs.  per  ton. 

Duration  of  stops,  15  seconds. 

Duration  of  coasting,  10  seconds. 

'  High  Speed  Electric  Railway  Problems  by  A.  H.  Armstrong,  A.  I.  E.  E., 
Vol.  XXII. 


MOTORS.  245 

Since  this  data  docs  not  take  into  consideration  grades  and 
curvature  or  other  vakies  of  acceleration,  deceleration,  etc.,  than 
those  listed,  either  a  large  number  of  such  charts  must  be  plotted 
or  the  results  taken  from  same  carefully  corrected  for  any  varia- 
tion of  actual  from  assumed  conditions. 

Method  Proposed  by  Storer/ — This  method  assumes  that  a 
certain  motor  has  been  tentatively  selected  and  that  it  is  desired 
to  determine  from  test  under  conditions  similar  to  those  of  actual 
service  whether  or  not  this  particular  motor  will  fulfill  the  require- 
ments. 

The  effective  current  for  the  various  runs  is  determined  as 
explained  above  and  the  average  voltage  at  the  terminals  of  the 
motor  found  from  the  voltage  time  curve.  If,  now,  the  motor 
be  operated  with  this  effective  current  and  w^ith  the  average 
voltage  impressed  upon  it,  the  motor  losses  will  be  the  same  as  in 
practice  and  the  heating  of  the  motor  under  service  conditions 
may  be  determined  therefrom.  It  should  be  remembered,  how- 
ever, that  the  ventilation  of  the  motor  is  better  in  service  and  it 
may  usually  be  depended  upon  to  carry  from  20  to  25  per  cent, 
more  load  with  the  same  temperature  rise  when  on  the  car.  This 
allows  a  good  factor  of  safety  if  the  motor  be  selected  from  test 
results. 

Method  Proposed  by  Hutchinson.^ — The  method  employed 
by  Hutchinson  where  a  large  number  of  motor  determinations 
are  to  be  made  by  a  manufacturing  or  an  engineering  company 
is  one  involving  mathematical  equations  based  upon  a  large 
number  of  general  charts  deduced  from  the  typical  speed  time 
curves.  In  place  of  assuming  the  straight  line  speed  time  curve 
of  Part  I,  Chapter  X,  to  be  correct,  a  mathematical  correction 
applying  to  the  difference  in  area  between  the  accurate  and  the 
straight  line  speed  time  curve  is  used  and  constants  derived  which, 
when  substituted  in  the  e(|uations  given,  enable  the  latter  to  be 
solved  for  correct  motor  capacity.  For  further  details  reference 
should  be  made  to  the  original  paper. 

*  By  N.  W.  Storer,  Street  Railway  Journal,  icjor. 
2  A.  I.  E.  E.,  Vol.  XXI. 


CHAPTER  IV. 
Types  of  Control. 

The  necessity  of  starting  a  car  by  first  impressing  a  low  voltage 
upon  its  motors  and  then  gradually  increasing  the  voltage  as  the 
motors  speed  up  until  they  are  receiving  their  rated  voltage,  has 
been  previously  explained.  The  advisability  of  maintaining  a 
constant  current  through  each  motor  during  the  constant  accelera- 
tion period  was  also  pointed  out.  It  is  now  necessary  to  consider 
the  various  standard  control  systems  which  have  been  devised 
to  accomplish  the  above  results. 

Rheostatic  Control. — The  earliest  type  of  control,  which  is 
now  practically  obsolete,  made  use  of  a  rheostat  in  series  with  the 
motors,  but  did  not  change  the  motor  connections  from  start  to 
full  speed.  Two  complete  revolutions  of  the  controller  handle 
were  necessary  to  cut  out  all  the  resistance,  but  the  rheostat  was 
so  designed  that  the  controller  handle  could  be  left  in  any  position 
indefinitelyandcorrespondinglysmall  variations  of  speed  obtained. 

Series  Parallel  Control. — Practically  all  the  control  systems 
in  use  with  direct  current  railway  motors  at  the  present  time,  al- 
though differing  widely  in  detail,  operate  upon  the  series  parallel 
principle.  The  two  motors  of  a  two  motor  equipment  or  those  of 
each  group  of  a  four  motor  ecjuipment  are  first  connected  in  series 
with  one  another  and  also  in  series  with  a  resistance.  This  resis- 
tance is  then  reduced  by  three  or  four  steps  until  the  two  motors 
are  alone  in  series  across  the  circuit  from  trolley  to  ground.  This 
notch  of  the  controller  is  termed  a  "running"  notch  as  the  con- 
troller may  be  left  in  this  position  continuously,  resulting  in  about 
half  speed.  With  the  next  step,  the  motors  are  changed  from 
series  to  parallel  connection  and  a  resistance  again  introduced. 
This  resistance  is  reduced  in  the  succeeding  steps  until  upon  the 
last  notch  all  motors  are  in  parallel  without  resistance.  This  is 
ordinarily  the  full  speed  position,  although  in  some  types  of  this 
control  an  additional  step  is  employed  which  shunts  the  motor 

246 


TYPES    OK    CONTROL. 


247 


field  with  a  resistance  and  thus  increases  the  speed  still  further. 
A  K-12  controller,  which  is  commonly  found  on  city  cars  with 
four  motor  equipments  is  shown  diagrammatically  with  motor  and 
resistance  connections  in  Fig.  loi.  The  connections  for  the 
various  notches  may  be  readily  traced  if  the  heavy  black  horizon- 
tal bands  representing  the  copper  sectors  on  the  control  cylinder 


Fig.    ioi. — K-i2\\'irin"  I^iagram. 


be  assumed  to  move  one  numbered  notch  to  the  left  for  each 
change  of  connections.  Care  should  be  taken  to  trace  out  the 
reversal  of  armature  connections  as  the  reverse  cylinder  repre- 
sented by  the  heavy  bands  at  the  right  of  the  figure  is  turned. 
The  switches  numbered  (19)  and  (15)  are  used  in  cutting  out  one 
set  of  motors  in  case  of  their  failure.     The  resistance  steps  are  so 


248  ELECTRIC   RAILWAY    ENGINEERING. 

proportioned  that  if  the  controller  is  steadily  "notched  up"  an 
approximately  constant  current  will  be  maintained  through  each 
motor.  A  diagrammatic  illustration  of  the  various  steps  is  found 
in  Fig.  102.  As  may  have  been  inferred  from  the  above  discus- 
sion, the  resistances  are  designed  to  remain  in  the  circuit  for  a 


Notch  Resist.  1  Arm.      IFld.  2  Arm.       2  Fid. 

1    ^AAAAAM3AAA/  nQsAAA^ 


■aaaaaA/XIVvw       \3/vw 


-I^aaaaaaTX^Vvvv         N^^AAAa- 


Transitioii 


J^AX/v^A^/^^sAA^/        \_Vvvv- 


Traiisition 


^^v\aavsa^(IVvw     '    nQv/Wv^ 


Transition 


La7sAAAAAXI)sAAA/       pQsA/VV 


A/V\Aaa/]X3sAA/^      'r^^SA/W 


-a^aaaA/tnQsaaa/    'pQvwv- 


■AAAAA/^^tXDvWV        |--0AA/V 


Fig.   102. 

short  time  only  and  will  therefore  overheat  if  they  be  left  in  circuit 
continuously. 

The  mechanical  construction  of  the  series-parallel  controller 
may  be  noted  from  Fig.  103  which  shows  the  interior  of  a  K-ii 
controller  with  asbestos  barrier  opened.  This  particular  con- 
troller has  been  provided  with  additional  barriers  by  the  operat- 
ing company  to  prevent  arcing  between  contacts.     The  main 


TYPES    OF    CONTROL 


?49 


drum  with  its  copper  sectors  insulated  from  the  shaft  and  engag- 
ing copper  contact  fingers  will  be  seen  on  the  left  and  the  reverse 
cylinder  of  similar  design  on  the  right  with  the  blow-out  magnet 
below.  A  sufficient  flux  is  produced  in  this  magnet  to  blow  out 
the  arc  which  is  formed  between  the  various  fingers  and  sectors 
as  the  circuits  are  opened.  At  the  bottom  will  be  found  the  motor 
cut-out  switches  and  the  connection  board. 

In  order  to  prevent  the  current  through  the  motors  from  being 
increased  too  rapidly  two  different  methods  are  used.  A  mechan- 
ical device  may  be  attached  to  the  top  of  the  controller   which 


Fig.   103. — K-ii  Controller. 


by  means  of  a  ratchet  and  pawl  prevents  the  forward  movement 
of  the  controller  handle  in  a  single  swing,  but  requires  a  slight 
backward  movement  at  each  notch  to  disengage  the  pawl  and 
thereby  allow  suflicient  time  for  the  current  to  decrease  to  its 
normal  accelerating  value.  The  second  method  involves  the  use 
of  a  specially  designed  controller  wath  a  limit  relay  through  which 
the  motor  current  passes.  Although  the  handle  may  be  thrown 
completely  around  in  a  single  swing,  this  movement  simply  puts 
a  coiled  spring  in  tension  which  "notches  up"  the  controller  as 
fast  as  the  interlocking  relay  will  permit.  When  the  current  falls 
to  a  predetermined  value  on  each  step  the  relay  unlocks  the  con- 


2SO 


ELECTRIC   RAILWAY   ENGINEERING, 


TYPES    OF    CONTROL. 


251 


trollcr  spindle  and  allows  it  to  progress  to  the  next  step  auto- 
matically. 

Master  Control. — With  the  rapid  increase  in  the  current 
required  by  the  motors  as  the  size  and  capacity  of  electric  railway 
equipment  advanced,  it  became  more  and  more  difficult  to  design 
a  controller  of  the  type  described  above  to  continually  break  these 
large  currents.  As  a  result  a  master  controller  is  often  found  in 
the  motorman's  cab,  quite  similar  in  principle  to  the  large  con- 


FiG.    105. — Contactor. 


trollers,  but  designed  to  control  an  auxiliary  circuit  only.  This 
auxiliary  circuit  operates  a  series  of  contactors  or  solenoid  operated 
main  switches  mounted  under  the  car.  With  such  a  system  the 
contactors  may  be  sufficiently  large  to  control  the  heavy  currents 
safely  and  little  room  is  required  for  equipment  above  the  floor, 
not  to  mention  the  reduction  in  the  amount  of  heavy  cable  de- 
manded by  such  an  eciuipment.  The  auxiliary  circuit  may  be  a 
high  resistance  circuit  supplied  from  the  trolley  or  in  some  in- 
stances it  is  supplied  by  a  storage  battery  of  about  14  volts. 


25- 


ELECTRIC    RAILWAY    ENGINEERING. 


Multiple  Unit  Control. — There  is  a  demand  in  elevated,  sub- 
way and  lieavy  interurban  service  for  the  operation  of  a  number 
of  cars  in  a  single  train  from  the  motorman's  cab  of  the  front  car. 
A  marked  advance  in  the  design  of  control  equipment  was  made, 
therefore,  when  the  multiple  unit  control  system  was  developed 
by  Sprague.  This  system  embodies  the  use  of  the  master  con- 
troller explained  above  not  only,  but  it  permits  the  contactors 
upon  all  cars  to  be  operated  simultaneously  by  the  master  control- 
ler of  a  single  car,  the  small  auxiliary  circuit  wires  alone  extending 
between  cars  through  the  agency  of  flexible  cables  and  pkig  con- 
tacts.    The  equipments  are  all  interchangeable  so  that  any  car 


Fig.  io6. — Unit  Switch  Group. 

may  be  made  a  control  car.  Fig.  104  represents  the  wiring  dia- 
gram of  both  the  main  and  auxiliary  circuits  of  the  multiple  unit 
control  in  detail,  while  Fig.  105  illustrates  the  contactor  with  its 
relay  contacts  at  the  bottom  and  its  asbestos  trough  for  the  circuit 
breaker  at  the  top. 

Unit  Switch  Control. — The  unit  switch  control  is  a  system 
developed  by  another  manufacturing  company  to  meet  the  require- 
ments of  master  control  of  single  car  equipment  or  of  multiple 
unit  control.  In  fact  upon  one  large  railway  system  cars  with 
the  unit  switch  control  and  the  Sprague  multiple  unit  control  are 
operating  interchangeably  in  the  same  train. 

The  unit  switch  control  differs  from  the  Sprague  multiple  unit 
system  principally  in  details  of  operation,  the  principle  of  the  two 


TYPES    OF    CONTROL. 


253 


being  the  same.  Both  systems  have  the  main  switches  and 
reversers  located  under  the  car,  the  operation  of  these  switches 
being  controlled  by  the  master  controller  and  an  auxiliary  or  relay 
circuit.  The  unit  switch  system  obtains  its  energy  for  the  auxil- 
iary circuit  from  one  of  two  14-volt  storage  batteries  carried  on 


Fig.   107 


-Unit  Switch  Master  Controller. 


the  car,  while  the  control  circuit  of  the  multiple  unit  system  is 
supplied  from  the  trolley.  In  the  former  system  the  main  switches, 
Fig.  106,  are  operated  by  air  pressure  obtained  from  the  main  air 
brake  reservoir,  the  air  valves  being  operated  by  the  battery 
circuit. 

The  automatic  "notching  up"  feature  of  the  unit  switch  sys- 
tem, which  may  also  be  secured  with  the  Sprague  multiple  unit 


2  54 


ELECTRIC    RAILWAY    ENGINEERING. 


control  is  accomplished  by  providing  the  main  switches  or  con- 
tactors with  relay  contacts  which  make  the  proper  connections 
in  the  auxiliary  circuit  as  they  open  or  close. 

The  master  controller  of  the  unit  switch  system,  Fig.  107, 
is  provided  with  three  forward  and  three  reverse  notches,  the 
function  of  which  will  be  more  clearly  seen  by  referring  to  Fig.  108, 


Line  t5Witch  q  ' 


Limit  Coil 


Fig.   ioS. 


which  is  a  much  simplified  connection  diagram.  The  first  notch 
closes  the  line  switch  (T)  and  the  unit  switches  (a)  and  (b),  thus 
putting  the  motors  in  series  with  all  resistance  in  circuit.  This  is 
not  a  permanent  running  notch,  but  the  train  maybe  thus  operated 
at  slow  speed  for  switching,  etc.,  for  a  short  time. 

The  second  notch  on  the  controller  is  the  full  scries  running 
position.     This  closes  switch  (C)  which  has  interlocking  contacts 


TYPES    OF    CONTROL.  255 

which  in  turn  close  (RR,).  The  latter  switch  carries  interlocks 
which  close  (RJ  and  so  on  closing  (RR,),  (R,),  (RR3),  (R3), 
etc.,  in  order,  cutting  out  corresponding  resistance  steps  until  the 
motors  are  in  series  without  resistance  between  trolley  and  ground. 

Notch  No.  3  or  the  full  parallel  running  position  closes  switch 
(d)  which  in  turn  breaks  the  auxiliary  circuit  of  (b)  and  the  latter 
switch  opens  together  with  all  the  resistance  switches  except  (c). 
When  (b)  has  completely  opened  it  causes  switches  (e)  and  (G) 
to  close.  When  these  are  fully  closed  their  interlocking  relays 
open  switch  (d).  When  (d)  is  again  open  the  circuits  through 
the  resistance  switches  (RRj),  (R,),  (RRJ,  etc.,  are  closed  con- 
secutively until  the  resistance  has  again  been  gradually  cut  out 
and  the  motors  are  finally  operating  in  parallel  across  the  line  with 
no  resistance.  Limit  relay  switches  described  above  prevent  the 
resistance  switches  from  closing  before  the  current  has  decreased 
to  its  normal  accelerating  value.  This  maintains  nearly  constant 
current  during  the  acceleration  period. 

In  some  forms  of  this  control  the  handle  of  the  master  controller 
is  automatically  returned  to  the  "off"  position  if  the  motorman 
takes  his  hand  from  same.  This  is  arranged  not  only  to  shut  off 
the  current,  but  also  to  apply  the  air  brakes  automatically.  With 
this  design  an  additional  coasting  notch  is  introduced  next  to  the 
"off"  position  for  which  the  current  is  oft",  but  the  brakes  are  not 
applied. 

A  complete  wiring  diagram  for  the  unit  switch  automatic  mul- 
tiple unit  control  system  including  both  auxiliary  and  main  cir- 
cuits will  be  found  in  Fig.  109,  but  because  of  its  complication 
the  simplified  diagram  of  Fig.  108  will  be  found  preferable  for  all 
but  detail  connections. 

It  must  be  remembered  that  in  all  multiple  unit  control  systems 
the  power  circuit  of  each  car  is  complete  in  itself,  with  indepen- 
dent contacts  with  trolley  or  third  rail.  Each  car,  therefore, 
must  have  its  own  limit  switch  which  may  be  adjusted  for  a  dif- 
ferent value  of  current  for  each  car  to  correspond  with  the  equip- 
ment upon  that  particular  car.  Provision  is  also  made  for  all  the 
switches  to  open  on  any  one  car  in  case  of  failure  of  power  on  that 
particular  car,  the  switches  "notching  up"  automatically  when 
the  power  is  again  supplied.     The  latter  feature  is  important  with 


256  ELECTRIC    RAILWAY    ENGINEERING. 

third  rail  operation  in  which  the  power  is  off  when  passing  over 
each  crossing. 

Alternating  Current  Control. — As  the  principal  advantage  in 
the  use  of  alternating  current  motors  on  the  car  is  the  possibility 
of  using  high  trolley  voltages  and  as  the  alternating  current  motors 
are  best  designed  for  low  voltage,  i.e.,  from  200  to  225  volts,  a 
transformer  must  be  used  on  the  car  to  reduce  the  trolley  voltage 
to  that  suitable  for  the  motors.  Since  taps  may  be  taken  from 
the  various  coils  of  this  auto-transformer  to  furnish  still  lower 
voltages  useful  in  starting  the  car  without  the  resistance  loss  en- 
tailed by  the  resistance  type  of  direct  current  motor  control  the 
principle  of  alternating  motor  control  differs  somewhat  from  those 
previously  explained. 

Alternating  current  control  systems  may  be  either  hand  oper- 
ated or  of  the  master  control  multiple  unit  type.  If  the  former,  the 
controller  is  similar  to  the  (K)  series  parallel  drum  controller 
with  the  exception  that  there  are  fewer  notches,  usually  five  or 
six  only,  and  no  series  parallel  connections.  The  magnetic  blow- 
out coil  is  also  omitted  as  the  alternating  current  arc  is  not 
difficult  to  extinguish  without  the  coil.  The  various  contacts 
made  between  controller  sectors  and  the  stationary  fingers  serve 
to  connect  the  motors,  generally  permanently  connected  two  in 
series,  to  the  various  taps  of  the  auto-transformer.  The  reversal 
of  the  motors  is  accomplished  in  the  same  manner,  the  reverse 
cylinder  reversing  either  the  armature  or  field  connections. 

With  the  master  alternating  current  control  the  principle  of 
operation  is  the  same  as  before.  The  magnetic  cores  of  the 
reverser  and  contactors  must,  however,  be  laminated  for  use  on 
alternating  current  circuits. 

In  order  that  connections  may  be  changed  from  one  transformer 
tap  to  another  without  opening  the  circuit  it  is  necessary  to  close 
a  local  circuit  through  a  portion  of  the  transformer  winding,  i.e., 
if  special  precautions  are  not  taken  a  short  circuit  will  be  formed 
in  a  portion  of  the  transformer  coil  as  two  taps  of  the  transformers 
are  connected  to  the  same  motor  terminal.  In  order  to  avoid  this 
difficulty  the  current  is  reduced  in  the  local  circuit  by  means  of 
"preventive"  resistance  or  reactance  leads  as  in  the  case  of  the 
single-phase  motor. 


TYPES    OF    CONTROL.  257 

The  auto-transformers  used  with  the  alternating  current  motor 
ecjuipments  have  been  standardized  for  3000,  6000,  and  10,000 
volts  trolley  potential  and  are  connected  directly  between  trolley 
and  ground,  the  motor  leads  being  connected  to  taps  near  the 
grounded  side  of  the  transformer.  The  transformer  is  of  the  oil 
cooled  type  and  is  mounted  under  the  floor  frame  of  the  car. 

Combined  Alternating  and  Direct  Current  Control.— 
As  previously  pointed  out  it  is  desirable  that  most  alternating 
current  interurban  roads  operate  cars  to  the  heart  of  the  terminal 
cities.  They  must,  therefore,  be  able  to  operate  upon  both  al- 
ternating and  direct  current.  In  order  that  the  control  ecjuip- 
ment  may  be  fitted  for  either  system  some  changes  in  detail  must 
be  made  and  a  considerable  complication  of  circuits  results.  The 
various  parts  of  the  apparatus  such  as  controller,  reverser,  con- 
tactors, etc.,  are  used  in  common  by  the  two  systems.  A  number 
of  changes  in  connections,  however,  must  be  made  in  shifting 
from  one  system  to  another.  These  are  principally  as  follows 
when  changing  from  alternating  to  direct  current  operation : 

Change  transformer  taps  to  resistance  taps. 

Change  main  fuses  or  circuit  breakers. 

Change  lightning  arresters. 

Introduce  the  magnetic  blow  out  into  the  circuit. 

Change  lighting  and  heating  circuits. 

Reconnect  fields  of  air  compressor  motor  for  series  operation. 
In  order  that  these  changes  may  be  made  in  one  operation  the 
cables  involved  are  connected  to  a  second  control  drum  similar  to 
the  main  controller.  This  is  styled  the  "commutating  switch," 
the  above  changes  being  made  by  a  simple  movement  of  the 
handle.  This  change  may  also  be  made  automatically  at  full 
speed  by  providing  a  release  for  the  switch  when  no  potential  is 
supplied  so  that  it  will  open  as  the  car  reaches  an  insulated  section 
in  the  trolley  between  the  alternating  and  direct  current  systems. 
The  switch  is  designed  to  reset  automatical!}  in  the  opposite  direc- 
tion as  the  direct  current  trolley  is  reached  and  vice  versa. 

As  may  be  inferred  from  the  above  an  added  complication 

enters  into  the  problem  in  operating  the  air  compressor  for  the 

air  brake  system.     In  some  installations  a  motor  generator  set  of 

small  capacity  is  installed  to  furnish  550  volts  direct  current  when 

17 


258  ELECTRIC    RAILWAY   ENGINEERING. 

supplied  with  alternating  current  from  the  transformer.  The 
standard  direct  current  air  compressor  may  then  be  used.  An- 
other method  more  often  found  is  to  design  the  compressor  motor 
for  both  alternating  and  direct  current,  connecting  the  field  coils 
in  parallel  for  the  former  supply  and  in  series  for  the  latter. 

Whereas  the  combination  of  the  two  control  systems  upon  one 
car  adds  considerable  complication,  as  wall  be  seen  from  Fig.  no, 
which  represents  the  complete  wiring  diagram  for  an  alternating 
current-direct  current  control  equipment,  and  although  the  first 
cost  and  maintenance  charges  are  necessarily  increased  thereby 
the  added  advantages  of  alternating  current  operation  apparently 
warrant  such  an  installation,  for  several  roads  are  successfully 
operating  such  an  equipment. 


Fig.  no,— Wiring  Diagram,  A-C.  D-C.  Control. 


CHAPTER  V. 

BlL^KES. 

The  problem  of  stopping  a  car  is  quite  as  important  as  that 
of  acceleration.  Since  the  kinetic  energy  of  the  car  must  be  over- 
come in  a  very  few  seconds  the  power  required  for  braking 
the  car  is  usually  many  times  that  rec[uired  for  accelerating. 
Whereas  the  rate  of  deceleration  and  energy  required  during 
the  braking  period  have  been  already  considered,  it  is  now 
necessary  to  study  the  braking  forces  more  in  detail  as  well  as  the 
various  types  of  equipment  which  have  been  designed  for  the 
production  and  control  of  such  braking  forces. 

Electric  cars  must  be  accelerated  and  retarded  by  virtue  of  the 
frictional  force  between  the  wheels  and  the  rails.  As  this  force 
is  proportional  to  the  weight  on  the  wheels,  the  available  force  is 
conveniently  found  from  the  ratio  of  horizontal  pull  in  pounds 
necessary  to  slide  the  wheels  on  the  rails  to  the  pressure  between 
wheels  and  rails.  This  ratio  is  commonly  termed  the  coefhcient 
of  friction.  It  has  been  found  to  vary  with  the  materials  in 
contact,  and  the  velocity  and  the  length  of  time  during  which  the 
force  is  applied. 

While  many  different  devices  have  been  tried  out  in  practice 
for  producing  the  necessary  frictional  forces  to  stop  a  car,  the  one 
which  is  now  almost  universally  used  in  both  electric  and  steam 
railroad  service  is  the  application  of  a  brake  shoe,  usually  of  cast 
iron  or  a  combination  of  cast  iron  and  other  materials,  to  the  treads 
and  flanges  of  the  car  wheels  by  means  of  either  hand  or  air  pres- 
sure transmitted  through  the  agency  of  a  carefully  proportioned 
system  of  levers. 

Coefficient  of  Friction. — An  experimental  study  of  the  cocfh- 
cient  of  friction  between  cast  iron  brake  shoes  and  steel  wheels 
under  practical  service  conditions  was  made  by  Galton  and 
Westinghousc  in  1878,  and  the  results  of  these  tests,  published  in 
the  1879  proceedings  of  the  Institution  of  Mechanical  Engineers, 
which  are  given  in  the  following  tables  have  been  ever  since  con- 

259 


26o 


ELECTRIC    RAILWAY    ENGINEERING. 


sidered  as  classic,  the  few  later  tests  which  have  been  made 
making  little  if  any  change  therein. 


TABLE  XXI. 

Coefficient  of  Friction  at  Various  Speeds  with  Cast  Iron  Brake  Shoes 

ON  Steel  Tires, 


cm 
is 

\ 

'elocity 

Coefficient  of  friction 

No.  of  tests  fr 
which  mean 

M.  p.  h. 

,       Ft 

.  p.  sec. 

Extreme 

taken 

Mean 

Max.       Min.  ' 

12 

60 

88 

.123 

058 

074 

67 

55 

81 

136 

060 

hi 

55 

50 

73 

153  ; 

050 

n6 

77 

45 

66 

179  t 

080  , 

127 

70 

40 

59 

194 

088 

140 

80 

35 

51 

197 

087 

142 

94 

30 

44 

196 

098 

164 

70 

25 

36.5 

205 

108  i 

166 

69 

20 

29 

240 

^33  1 

192 

78 

15 

22 

280  ! 

131   1 

223 

54 

10 

14-5 

281 

161 

242 

28     • 

7-5 

II 

325 

123 

244 

20 

Under  5 

Just  moving 

. .  .    Under  7 

Tnsf  mnvinp    .  . 

340 

156 

273 
330 

TABLE  XXII. 

Effect  of  Elapsed  Time  on  Coefficient  of  Friction. 


Speed 

Coefficient  of  Friction 

M.  p.  h. 

Start 

After  5  sec. 

After  10  sec. 

After  15  sec. 

After  20  sec. 

20 

27 
37 
47 
60 

.182 
.171 

•152 
.132 
.072 

•  152 

•130 
.096 
.080 

■^33 
.119 
.083 

.116 
.081 
.069 

.099 
.072 

.06^                       ocS 

BR.A.KES.  26l 

From  the  above  tables  the  maximum  pressure  to  be  applied 
to  the  brake  shoes  may  be  determined  under  the  various  service 
conditions  in  order  to  provide  the  required  frictional  tangential 
force.  To  determine  what  the  limits  of  the  latter  are  the  coeffi- 
cient of  friction  between  wheels  and  rail  must  be  known.  This 
value  varies  widely  with  the  condition  of  the  rail,  but  may  be 
safely  assumed  from  0.15  to  0.30  when  the  rail  is  wet  and  dry 
respectively.  These  latter  values  are  coefficients  of  static  friction 
which  are  greater  than  dynamic  friction  if  other  conditions  are  the 
same.  For  if  the  wheels  are  rolling,  there  is  no  relative  sliding 
between  wheels  and  rails  and  the  frictional  force  to  be  considered 
is  that  necessary  to  start  one  body  from  rest  upon  the  other  and 
not  that  lesser  force  necessary  to  keep  one  body  in  motion  upon 
the  other.  The  maximum  limit  of  brake  shoe  friction  is  now  at 
once  apparent,  for  it  must  not  exceed  the  static  friction  between 
wheels  and  track.  If  it  were  to  exceed  that  value  the  brake 
shoes  would  "lock  the  wheels"  and  the  latter  would  "skid"  on 
the  rails  with  increased  instead  of  lessened  speed  because  of  the 
lower  value  of  dynamic  friction  thus  suddenly  brought  into 
play  between  wheels  and  track. 

Theoretically,  cars  should  be  ec|uipped  with  braking  apparatus 
which  will  be  able  to  approximate  as  nearly  as  possible  this  maxi- 
mum value  for  emergency  stops,  but  since  the  braking  force  with 
hand  brake  equipment  depends  upon  the  strength  of  the  motor- 
man  and  with  air  brake  equipment  upon  the  variable  air  pressure, 
it  is  usually  possible  to  "skid  the  wheels"  on  the  average  car  if 
the  brakes  are  applied  too  forcibly.  Further,  since  Table  XXI 
shows  that  the  friction  between  brake  shoe  and  wheel  increases 
as  the  speed  decreases  during  the  braking  period,  a  force  applied 
to  the  brake  shoes  when  braking  is  commenced  which  is  slightly 
less  than  that  necessary  to  lock  the  wheels  may  become  suffi- 
ciently great  to  produce  that  result  at  lower  speeds  for  the  reason 
that  the  static  friction  between  wheels  and  track  remains  constant. 
Every  experienced  motorman  understands  the  results  of  such  an 
application  of  biakes  and  releases  and  reapplies  the  braking  pres- 
sure with  less  and  less  intensity  as  the  car  comes  to  a  stop.  Fail- 
ure to  do  this  results  in  too  sudden  a  stop  for  comfort,  a  severe 


262 


ELECTRIC    RAILWAY   ENGINEERING. 


chattering  of  the  brake  rigging  and  possible  skidding,  and  in- 
cidentally marks  an  inexperienced  or  careless  motorman. 

Another  factor  which  must  be  taken  into  consideration  in 
stopping  a  car  comfortably  and  safely  is  the  condition  of  the  track, 
the  sudden  and  unexpected  skidding  of  wheels  and  the  conse- 
quent sudden  increase  in  speed  having  been  the  cause  of  many  an 
accident.  It  is  a  peculiar  fact  that  with  a  very  thin  film  of  water 
on  the  rail  due  to  a  slight  shower,  the  friction  is  greatly  reduced 
over  that  of  a  dry  rail  or  even  a  thoroughly  wet  rail.  Again  the 
crushing  of  leaves  or  weeds  on  the  tread  of  the  rail  or  too  generous 
a  supply  of  track  grease  often  make  it  impossible  to  stop  on  a 
section  of  track  thus  affected  without  the  use  of  sand.     Cars 


Fig.   III. 


have  been  known  to  slide  down  long  hills  with  tracks  thus  covered 
while  the  motorman  was  utterly  powerless  to  reduce  the  speed, 
even  with  the  reversal  of  the  motors.  Most  roads,  therefore, 
provide  a  generous  supply  of  sand  on  each  car  not  only,  but 
require  the  track  repair  crew  to  keep  the  track  free  from  leaves, 
grass  and  weeds. 

Braking  Forces. — If  the  car  is  to  be  stopped  by  the  appli- 
cation of  pressure  to  the  brake  shoes  bearing  upon  the  car  wheels 
as  is  ordinarily  the  case,  it  will  be  noted  at  once  that  the  forces 
tending  to  move  the  car  forward  and  those  applied  as  resistances 


BRAKES. 


263 


to  stop  the  motion  do  not  lie  in  the  same  horizontal  plane,  the 
former  acting  at  the  center  of  gravity  of  the  combined  loaded  car 
body  and  trucks  and  the  latter  at  the  contact  between  wheels 
and  rails.  The  result  is  easily  seen  to  be  a  tendency  to  raise  the 
rear  of  the  car  from  the  track,  the  forces  acting  at  the  center  of 
gravity  of  the  car  having  a  moment  about  the  front  truck.  In 
addition,  t  lere  is  a  tendency  for  the  rear  wheels  of  each  truck  to 
lift  from  the  track  for  the  reason  that  the  forces  at  the  king  pin 
and  center  of  gravity  of  the  truck  have  a  moment  about  the  front 
wheels.  The  resulting  effect  is  that  the  pressure  is  lessened 
between  car  and  rails  at  the  rear  and  the  static  friction  depended 
upon  for  braking  thereby  reduced.     Either  the  braking  pressure 


J'k;.    I  ij. 


must  be  reduced  upon  the  rear  truck  over  that  of  the  front  truck 
and  that  of  the  rear  wheels  of  each  truck  over  that  of  its  front 
wheels  or  else  all  braking  pressures  must  be  lowered  considerably 
below  that  possible  at  the  front  end  of  the  car.  That  the  braking 
pressures  on  the  rear  truck  cannot  be  made  less  than  those  of  the 
front  truck  by  any  change  in  the  leverages  on  the  car  in  the  case 
of  double-end  cars  is  obvious.  With  single-end  interurban  cars 
such  provision  is  often  made.  There  is,  however,  a  method  of 
hanging  brake  shoes  with  the  supporting  link  of  the  brake  shoe  out 
of  line  with  the  tangent  to  the  wheel  at  the  center  of  the  shoe 


>64 


ELECTRIC    RAILWAY    ENGINEERINXJ. 


which  will  vary  the  pressure  between  shoe  and  wheel  with  the 
direction  of  operation  of  the  car.  This  rpay  be  illustrated  by 
referring  to  Fig.  in  where  the  brake  shoe  hanger  is  5°  out  of  line 
with  the  tangent.  With  the.  car  moving  toward  the  right  the 
frictional  force  at  the  shoe  is  balanced  by  a  force  of  compression 
in  the  hanger  plus  a  force  normal  to  the  car  wheel  proportional 
to  the  sine  of  5°.  This  is  added  directly  to  the  brake  shoe  pres- 
sure. If  the  car  be  operating  toward  the'  left,  thus  making  the 
wheel  shown  in  the  figure  the  rear  wheel  of  the  truck,  the  frictional 
force  produces  a  tension  in  the  brake  shoe  hanger  and  a  force . 
proportional  to  the  sine  of  5°  tending  to  reduce  the  pressure  ex- 
erted by  the  brake  rigging.  Whereas  this  effect  may  be  increased 
by  increasing  the  angle  between  brake  shoe  hanger  and  tangent, 
too  great  an  increase  of  this  angle  tends  to  bind  the  shoes  upon 


Direction  ol  Motion 


nm 


Fig.   113. 


the  wheel  as  in  the  case  of  a  toggle  joint  causing  chattering  of  the 
brake  rigging  and  fiat  wheels.  Such  a  condition  often  found  on 
car  trucks  is  Illustrated  in  Fig.  112,  where  the  angle  has  been 
increased  to  30°. 

In  order  to  determine  the  concrete  value  of  the  resultant 
weight  upon  each  wheel  of  a  car,  it  is  necessary  to  analyse  all  the 
forces  acting  thereon  as  outlined  in  Fig.  113  and  to  balance  the 
moments  of  the  forces  about  any  single  point  as  in  any  problem 
in  mechanics.  A  sufficient  number  of  equations  will  result  to 
permit  the  weights  (WJ,  (W,),  (W3)  and  (WJ  to  be  calculated 
and  the  corresponding  frictional  forces  (FJ,  (F^),  (F3),  and  (FJ 
determined  through  the  agency  of  the  coefficient  of  friction.  In 
determining  the  above  equations,  it  must  be  remembered  that 


BRAKES. 


265 


the  rotative  inertia  of  the  car  wheels,  axles,  and  motor  armatures 
must  be  overcome  in  stopping  the  car  as  well  as  the  translational 
inertia  6i  car  and  trucks. 

Whereas,  the  method  abo^■c  outlined  will  result  in  a  very  ac- 
curate analysis  of  the  Various  weights  and  forces  involved,  it 
would  be  seldom  indeed,  that  the  electrical  engineer  would  make 
such  a  calculation  before  writing  specifications  for  car  ecjuipment. 
The  effect  of  reduction  of  pressure  at  the  rear  of  the  car  may  be 
taken  roughly  at  15  per  cent,  and  the  brake  rigging  designed  for  a 
resultant  brake  shoe  pressure  corresponding  to  85  per  cent,  of 
the  actual  static  weight  on  wheels. 

Braking  Equipment. — It  has  been  previously  stated  that  the 


Brake  Cylinder 


Fig.  114. 


hand  and  air  brake  systems  are  now  almost  universally  used  in 
electric  railway  service.  The  former  is  used  alone  upon  small 
city  cars,  while  both  systems  are  universally  applied  to  the  heavier 
suburban  and  interurban  equipment.  Where  both  are  used  the 
same  brake  rigging  is  installed  for  both,  the  leverages  in  the  case 
of  the  hand  brake  being  greater  to  make  up  for  the  relatively 
small  pull  the  motorman  can  exert  as  compared  with  the  air 
pressure  of  the  brake  cylinder.  A  typical  brake  rigging  installa- 
tion may  be  seen  in  Fig.  114,  the  operation  of  which  will  be  self- 
explanatory  if  it  be  stated  that  the  piston  of  the  air  brake  cylinder 
is  forced  forward  by  air  pressure,  when  the  proper  valve  position 
is  provided  by  the  motorman,  just  as  the  piston  of  a  steam  engine 
is  operated.  The  principal  dimensions  of  the  various  parts  of 
the  equipment  of  several  interurban  cars  of  the  Middle  West  are 
given  in  Table  XXIII,  all  of  which  refer  to  Fig.  114.  The  ratio 
between  brake  shoe  pressure  and  brake  cylinder  pressure  may  be 


266 


ELECTRIC    RAILWAY   ENGINEERING. 


readily  obtained  from  the  following  equations.  With  this  ratio 
known  the  air  brake  pressure  per  square  inch  of  piston  area  may 
be  quickly  determined  for  various  desired  brake  shoe  applications. 

TABLE  XXIII. 
Dimensions  of  air  Brake  Equipment. 


Dimensions  of  levers  in  inches 


Interurban 
car 

A               B               CD              E               F 

G 

I 

2 

3 

4 

10.5            9.0      5.0          16.0           4.0 

9-5           9-5      70         18.0           7.0 

12.0         23.0      6.0         16.0           5.0 

II. 0         17.0           35             5.0         12.5           5.0 

13.0 

18.0 
15-0 

12.5 

Let  (P)  represent  the  total  force  on  the  piston  of  the  brake 
cylinder  and  designate  the  resultant  forces  in  the  various  links^ 
by  the  letters  appearing  upon  the  links  in  Fig.  114. 

P  =  xA-ir  pressure  X  area  piston.  (103) 

From  the  ratios  of  lever  arms  the  following  equations  may  be 
derived : 

A.     W     PA  .       . 

Y=      =  (104) 

2      2B 

_     Y(D  +  E)  ,       , 

T  =  ^^--^  (105) 

YE 
V=  (106) 

D 

^,^V(F  +  G)  (107; 

G 
If  the  ratio  between  total  pressure  exerted  by  all  brake  shoes 
to  brake  cylinder  pressure  be  signified  by  (R). 

R  (for  a  double-truck  car)  = (108) 

Substitution  in  the  above  equations  of  values  for  the  four  cars 


BRAKES.  267 

in  Table  XXIII  results  in  the  forces  listed  in  Table  XXI\'  with 
a  10  in.  cylinder  and  maximum  air  pressure  of  70  lb.  per  sq.  in. 

TABLE  XXIV. 
Forces  Acting  in  Air  Br^ke  Equipment. 


Forms  in 

pounds 

Interurban 

car 

P 

W 

Y 

T 

V 

T' 

R 

I 

5.497 

6,400 

3,200 

13,450 

10,250 

13,400 

19.6 

2 

5,497 

5,497 

2,748 

9,830 

7,080 

9,830 

14.4 

3 

5,497 

2,860 

1,430 

5,250 

3,820 

5,100 

7-54 

4 

5,497 

3,550 

1,775 

6,210 

4,430 

6,210 

9.06 

From  the  above  table  it  will  be  seen  that  the  multiplying  power 
of  the  brake  levers  on  four  interurban  cars  taken  at  random 
varies  from  7.5  to  19.5. 

It  should  not  be  forgotten  that  the  above  forces  are  based  upon 
an  emergency  application  of  air  of  70  lb.  pressure  which  is  seldom 
used.  For  an  ordinary  service  application  the  forces  would 
average  less  than  one-half  the  above  values. 

A  further  calculation  may  be  made  from  Table  XXIII  which 
is  of  value  in  determining  the  adequacy  of  the  equipment  for  the 
service.  Car  No.  4  in  this  table  weighs  in  the  neighborhood  of 
25  tons.  The  total  brake  shoe  pressure  exerted  on  all  wheels 
with  a  70  lb.  application  of  air  is 

8  X  6,210  =  49,680  lb. 

Ratio  of  total  brake  shoe  pressure  to  weight  of  car  is  99.  2  per  cent. 
If  the  coefficient  of  friction  were  the  same  between  shoe  and  wheels 
that  it  is  between  wheels  and  rails  it  would  be  possible  to  skid 
the  wheels  with  an  application  of  air  slightly  above  70  lb. 

Brake  Rigging. — The  levers  by  means  of  which  the  braking 
force  is  transmitted  from  hand  brake  or  brake  cylinder  to  brake 
shoes  are  of  heavy  strap  iron  linked  together  with  steel  pins 
provided  with  cotter  pins  and  supported  from  the  under  frame  of 
the  car  by  means  of  strap  iron  stirrups.     Links  in  tension  are 


268 


ELECTRIC    RAILWAY    ENGINEERING. 


usually  constructed  of  i  in.  round  iron  rod.  The  circle  bar 
between  links  (Y)  and  (W)  Fig.  114  is  provided  with  the  truck 
together  with  a  clevis  which  may  be  welded  to  rod  (W)  and 
which  is  so  designed  as  to  slide  on  the  circle  bar  as  the  trucks 
swing  with  respect  to  the  car  body  when  turning  a  curve. 

The  hand  brake  consists  of  the  familiar  vertical  ratchet  crank 


Fig.  115. — Straight  Air  Brake  Equipment. 


or  wheel  in  the  motorman's  cab  which  winds  up  a  chain  under 
the  car  vestibule,  this  chain  exerting  a  tensile  force  at  H,  Fig.  114. 
Straight  Air  Brake  Equipment. — The  air  brake  equipment 
in  its  simplest  form  consists  of  a  motor  driven  air  compressor,  a 
storage  reservoir,  a  brake  cylinder,  a  governor,  two  engineer's 
valves  with  gauges  for  double  end  equipment,  a  system  of  levers, 


BRAKES.  269 

complete  piping  equipment  and  usually  one  or  more  air  whistles 
to  act  as  signals.  Fig.  115  represents  the  apparatus  above  out- 
lined. The  compressor,  reservoir,  brake  cylinder  and  piping  are 
supported  from  the  under  frame  of  the  car.  The  governor  is 
often  placed  on  the  car  floor  under  one  of  the  end  seats,  while  the 
remainder  of  the  equipment  is  in  the  motorman's  cab. 

The  air  compressor  is  a  direct  connected  pump  and  direct 
current  550  volt  series  motor  connected  between  trolley  and 
ground  with  only  a  snap  switch,  the  governor  switch  and  a  fuse 
in  circuit.  The  trolley  connection  is  made  between  circuit 
breaker  and  trolley  so  that  the  compressor  will  not  stop  when 
the  circuit  breaker  opens. 

The  governor  is  a  pneumatically  operated  switch  which  can  be 
adjusted  to  close  the  compressor  circuit  and  thereby  start  the 
compressor  when  the  air  pressure  falls  below  a  predetermined 
value  and  which  will  automatically  stop  the  compressor  when  the 
pressure  reaches  the  maximum  value  desired.  While  there  is  a 
considerable  range  for  which  the  governor  may  be  adjusted,  it 
is  generally  set  to  operate  at  about  70  and  90  lb.  per  sq.  in. 
respectively. 

The  motorman's  valve  is  of  the  three  position  type.  The 
operating  handle,  when  moved  to  the  "service"  position  opens 
the  valve  between  reservoir  and  brake  cylinder  and  applies  the 
brakes.  The  extent  to  which  the  handle  is  moved  in  this  direction 
and  the  time  during  which  it  is  left  there  determine  the  pressure 
applied  to  the  brake  shoes.  If  it  be  desired  to  retain  this  pressure 
in  the  brake  cylinder  the  handle  may  be  moved  to  the  "lap" 
position  where  all  valves  are  closed.  The  handle  may  be  re- 
moved only  when  in  this  position.  By  throwing  the  handle  to 
the  position  opposite  to  that  of  "service"  into  the  "exhaust" 
notch  the  air  in  the  brake  cylinder  escapes  to  the  atmosphere 
and  the  brakes  are  released.  It  is  a  rather  unfortunate  fact 
that  two  types  of  air  brake  valves  apply  the  air  with  opposite 
movements  of  the  valve  handle.  This  is  rather  confusing  to 
motormcn  accustomed  to  one  method  when  changing  to  another 
road  using  the  other  system. 

Automatic  Air  Brake  Equipment. — Contrasted  with  the 
above  "  straight  air  brake  equipment"  which  is  applicable  to  single 


270  ELECTRIC    RAILWAY   ENGINEERING. 

cars  only,  the  "automatic  air  brake  equipment"  similar  to  that 
found  on  steam  trains  is  often  found  on  electric  lines,  especially 
in  elevated,  subway,  and  heavy  interurban  service  where  two  or 
more  cars  are  coupled  together.  The  principal  difference  be- 
tween this  system  and  the  one  previously  described  is  the  addition 
of  a  second  or  auxiliary  storage  reservoir  and  the  use  of  a  "  triple 
valve."  A  "train  line"  or  continuous  pipe  under  air  pressure  is 
provided  throughout  the  train,  rubber  hose  couplings  with  pat- 
ented air  tight  knuckle  joints  permitting  the  ready  closing  of  the 
line  when  shifting  cars.  The  "triple  valve,"  which  is  the  vital 
part  of  the  entire  system,  consists  of  a  piston  valve  ordinarily 
balanced  in  a  mid  position  by  the  auxiliary  reservoir  pressure 
on  one  side  and  the  "train  line"  pressure  on  the  other.  A^Hien 
the  motorman's  valve  is  in  the  "service"  position  the  train  line 
is  momentarily  opened  to  the  atmosphere  and  its  pressure  re- 
duced sufficiently  to  cause  the  auxiliary  reservoir  pressure  to  move 
the  triple  valve  piston  to  such  a  position  as  to  admit  air  from  the 
auxiliary  reservoir  to  the  brake  cylinder  and  apply  the  brakes. 
This  occurs  on  every  car  of  the  train.  To  release  the  brakes 
the  motorman's  valve  in  the  "exhaust"  position  allows  air  to 
flow  from  the  main  reservoir  to  the  train  line  and  raise  its  pressure 
so  that  the  triple  valve  is  again  balanced  and  the  brake  cylinder 
opened  to  the  atmosphere.  One  of  the  most  valuable  features 
about  this  equipment  is  the  fact  that  any  leakage  or  breaking 
apart  of  cars,  etc.,  which  will  reduce  the  pressure  in  the  train  line 
will  set  the  brakes  upon  all  cars  of  the  train. 

Quick  Action  Automatic  System. — The  automatic  air  brake 
as  above  described  is  applicable  to  trains  up  to  about  five  cars  in 
length.  For  the  longer  trains,  however,  the  reduction  in  train 
line  pressure  requires  an  appreciable  time  to  be  felt  throughout 
the  length  of  the  train.  The  resulting  effect  of  some  cars  of  the 
train  braked  with  others  free  causes  severe  strains  on  the  draft 
rigging,  not  to  mention  inconvenience  to  passengers.  The  "  quick 
action  automatic  air  brake  system"  is  therefore  applied  to  the 
longer  trains.  This  is  similar  to  the  other  with  the  exception 
that  the  "triple  valve"  is  so  designed  as  to  feed  both  auxiliary 
reservoir  and  train  line  pressure  into  the  brake  cylinder.  This 
procedure  not  only  causes  each  car  to  aid  in  quickly  reducing 


BR.\KES. 


271 


the  train  line  pressure  throughout  the  train,  but  it  decreases  the 
drop  in  train  line  pressure  which  must  be  produced  at  the  head 
car.  In  other  words  the  action  is  cumulative  throughout  the 
length  of  the  train. 

In  both  the  automatic  systems  the  motorman  is  pro^•ided  with 
a  duplex  gauge  indicating  both  train  line  and  main  reservoir 
pressure.  In  the  straight  air  brake  system  either  a  single  gauge 
hand  is  provided  to  denote  the  reservoir  pressure  or  two  indica- 
tions are  given,  one  above  outlined  and  in  addition  a  second  hand 
to  show  the  pressure  applied  to  the  brake  cylinder. 

Friction  Disc,  Electric  and  Track  Brakes. — Many  types  of 
special  braking  devices  have  been  invented  and  tried  out,  involv- 
ing friction  discs  bearing  upon  the  planed  inside  surfaces  of  car 
wheels,  magnetic  brakes  supplied  with  energy  either  from  the 
trolley  or  the  car  motors  used  as  generators,  and  track  brakes 
consisting  of  shoes  bearing  upon  the  rail  instead  of  the  car  wheels 
and  often  designed  to  grip  the  head  of  the  rail  with  a  variable 
pressure.  WTiile  some  of  these  devices  have  served  admirably 
in  special  instances,  especially  as  an  additional  safety  device  upon 
severe  grades,  they  are  not  in  sufficiently  general  use  to  warrant 
detailed  description. 

Reversal  of  Motors. — A  method  of  stopping  cars  in  cases  of 
emergency,  known  as  "reversing"  consists  in  throwing  the  re- 
verse lever  to  the  reverse  position  and  applying  power  to  the 
extent  of  one  or  possibly  two  series  notches  of  the  controller. 
This,  of  course,  tends  to  operate  the  car  in  the  reverse  direction 
and  not  only  stops  the  car  with  a  sudden  jolt  but  is  likely  to  damage 
the  car  equipment.  It  is  therefore  seldom  resorted  to,  but  in 
case  of  failure  of  the  brake  rigging  or  to  avoid  a  collision,  it  is 
sometimes  a  valuable  protection. 

Motors  used  as  Generators. — As  a  last  resort,  with  no  power 
supplied  to  the  car,  and  with  brake  rigging  damaged,  there  is 
yet  another  method  of  stopping  the  car.  The  reverse  lever  mav 
be  thrown  into  the  reverse  position  and  the  controller  handle 
swung  into  one  of  the  parallel  notches.  The  resulting  connection 
causes  one  motor  to  operate  as  a  generator,  driven  bv  the  inertia 
of  the  car,  thus  supplying  the  other  motor  with  power  tending 
to  operate  the  car  in  the  reverse  direction.     This  method  mav, 


272 


ELECTRIC    RAILWAY    ENGINEERING. 


of  course,  be  used  if  the  power  supply  be  present  by  throwing  the 
circuit  breaker  to  the  open  position. 

With  either  of  the  above  methods  involving  the  use  of  electric 
power  in  stopping  the  car,  great  care  must  be  taken  not  to  skid 
the  wheels  as  this  condition  prevents  a  prompt  stop  not  only,  but 
is  likely  to  flatten  the  wheels  as  well. 

Brake  Tests. — It  is  often  of  great  value  to  know  the  time  and 


300 

I 

10 

160 

10 

S 

1:.>U 

30 

6 

SO 

30 

4 

40     10 


distance  required  in  which  to  stop  cars  of  various  weights  operat- 
ing at  different  speeds.  This  is  particularly  true  in  case  of 
accidents  and  court  litigation.  Whereas  these  facts  may  be 
predetermined  mathematically  as  has  been  previously  pointed 
out,  the  actual  test  of  a  car  in  service  is  often  rec[uired  as  well. 


BRAKES. 


273 


In  order  to  carry  out  such  a  test  thoroughly,  it  is  necessary  to 
provide  a  method  of  determining  speed  of  car,  time  between 
brake  signal  and  stop  and  distance  travelled  during  this  period. 
It  is  also  well  in  some  cases  to  know  the  air  brake  pressure,  the 
amount  of  wheel  skidding  and  the  motor  current  in  case  either  of 
the  reverse  methods  are  used. 


10 


^ 

9 

to 

2 

3 

8 

■■io 

2 

* 

■iO 

60 

G 

io      oO     5 


13      30     3 


10      20     -2 


10      ] 


1 

1 

N 

EMERGEMCYSTOP 

FROM 

FULL  SERIES  POSITION 

\sp 

eed 

N 

^ 

^ 

)  Dista 

ice 

y- 

:> 

/ 

cyx^ 

^ 

A 

\ 

\ 

/ 

\ 

\.       \ 

)Decel 

sratior 

1 

/ 

/ 

^ 

)\ 

)Air  P 

ressur 

2 

// 

y 

^ 

\ 

t^ 

\ 

8  4 

Seconds 


Fig.  117. 


One  of  the  most  satisfactory  methods  of  determining  the  speed 
at  any  instant  is  by  means  of  a  magneto  generator,  driven  from 
the  car  axle,  the  voltage  of  the  generator  read  from  a  voltmeter 
in  circuit  being  directly  proportional  to  speed. 

The  distance  travelled  during  the  braking  period  may  be 
roughly  determined  from  the  revolutions  of  the  car  wheel  or  a 
similar  wheel  driven  from  the  car  axle,  which  may  be  caused  to 
make  electrical  contacts  every  revolution.  If  any  skidding 
occurs,  this  method  becomes  valueless.     A  method  which  has 


2  74 


ELECTRIC    RAILWAY   ENGINEERING. 


worked  admirably  in  recent  tests  at  Purdue  University  is  to  give 
the  braking  signal  by  means  of  a  revolver  from  which  a  ball  is 
shot  beside  the  track,  thus  marking  the  start  of  the  braking  test 
very  accurately.  The  distance  required  to  stop  may  then  be 
measured  along  the  track  from  this  point  with  a  steel  tape. 


-LJ     11f1 

J 

GENERATED  MOTORS 

FROM 

FULL  PARALLEL  POSITION 

100 100 

/ 

90  90  :C 

r 

pN 

)  Current  per  Moto: 

80  80   10 

V^ 

J 

\ 

( 

V 

)  Acti 

al  Dis 

-ance 

60  GO  13 

N 

k- 

50  50   10 

N 

ks, 

leed 

.40  40      8 

\ 

C 

\, 

\ 

^ 

I 

)  Distance 

30  30     6 

■ 

20  20     4 

/ 

/ 

\ 

10  10     2 

A 

L 

. — 

\ 

v 

)Deee 

eratlo 

1 

^ 

r^ 

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01234567 
Seconds 
Fig.  ii8. 

All  of  the  data  of  the  test  may  readily  be  arranged  for  an  auto- 
matic graphical  record  upon  a  single  paper  chart,  thus  illustrating 
clearly  the  desired  values  at  any  given  instant. 

The  results  of  such  tests  are  best  shown  by  curves  similar  to 
those  of  Figs.  ii6,  117,  and  118  which  represent  braking]]tests 
made  with  the  Purdue  University  Test  Car^  of  approximately 

'  Thesis,  Purdue  University,  19  ii,  by  Luhrman,  Blaschke  and  McLean. 


BIL\KES.  275 

25  tons  weight  equipped  with  brake  rigging  designated  as  car 
No.  4  in  Table  XXIII.  While  it  is  believed  that  these  figures 
are  in  general  self-explanatory,  especial  attention  should  be 
called  to  the  amount  of  skidding  which  took  place  in  the  stop  by 
means  of  generated  motors,  Fig.  118,  and  also  to  the  fact  that 
the  speed-time  curve  is  seldom  a  straight  line  as  is  assumed  in 
theoretical  calculations.  The  error  in  such  an  assumption,  how- 
ever, is  obviously  small. 

The  results  of  all  the  tests  made  upon  the  above  car  arc  given 
in  some  detail  in  Table  XX\"  and  may  prove  of  some  value  in 
approximating  possible  stopping  time  and  distance  under  other 
conditions. 


276 


ELECTRIC    RAILWAY    ENGINEERING. 


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CHAPTER  \T. 
Car  House  Design. 

As  the  modern  car  house  not  only  provides  storage  for  the 
rolling  stock,  but  also  furnishes  room  for  inspection  and  repairs 
and  often  includes  the  shops  and  offices  of  the  railway  company, 
much  thought  must  be  given  to  its  location  and  design. 

Location. — Too  often  a  lot  for  a  car  house  is  secured  before 
the  size  or  requirements  of  the  latter  are  determined,  thus  re- 
quiring that  the  car  house  and  track  layout  be  fitted  to  the  lot. 
This  procedure  results  in  a  limited  and  unsatisfactory  design. 
A  site  of  sufficient  size  for  all  the  above  functions  of  the  car  house, 
with  proper  consideration  for  future  growth,  should  be  selected 
in  the  most  convenient  section  of  the  city  from  an  operating 
standpoint.  Care  must  be  taken  to  make  sure  that  all  necessary 
track  privileges  may  be  obtained  from  the  city  authorities  before 
the  site  is  finally  purchased. 

In  the  case  of  the  interurban  car  house,  a  location  for  the  latter, 
together  with  the  shops,  offices  and  often  the  power  house  or 
substation  is  selected  at  about  the  middle  of  the  line,  although 
where  the  interurban  road  is  operated  by  the  company  controlling 
the  traction  systems  of  the  terminal  cities  the  cars  may  be  handled 
by  the  city  car  houses.  This  plan  often  offers  the  advantages  of 
lessened  fire  risk,  smaller  dead  mileage  of  cars,  improved  freight 
and  express  accommodations  and  better  or  more  congenial  homes 
for  employees.  For  the  advantages  to  be  gained  by  locating  near 
the  power  house,  as  well  as  for  an  outline  of  many  considerations 
to  be  taken  into  account  in  deciding  upon  the  proper  location, 
reference  should  be  made  to  Chapter  V  of  Part  H. 

The  fire  risk  of  a  car  house  is  great  and  abundant  water  supply 
and  other  fire  protection  should  be  available  not  only,  but  care 
should  be  taken  to  avoid  all  fire  risk  from  adjoining  buildings. 
The  sub  soil  should  be  examined  with  a  view  toward  determining 
the  foundations  and  piling  necessary,  although  with  the  lighter 

277 


278  ELECTRIC    RAILWAY    ENGINEERING. 

and  more  equally  distributed  weight  of  the  car  house  this  is  not 
such  a  vital  factor  as  with  the  power  station.  Good  drainage 
and  suitable  sewer  connections  should,  however,  be  available  or 
easily  provided. 

Layout  of  Tracks. — One  of  the  first  questions  to  be  decided 
is  the  percentage  of  total  cars  owned  for  which  cover  shall  be 
provided.  This  is  a  question  upon  which  railway  managers 
differ  widely.  At  the  1907  Convention  of  the  American  Street 
and  Interurban  Railway  Association  a  committee  appointed  to 
investigate  this  question  assumed  the  case  of  a  car  house  accom- 
modating 84  cars  under  cover  as  compared  with  a  similar  design 
capable  of  housing  but  one-third  this  number.  The  estimated 
costs  were  $105,000  and  $45,000  respectively.  With  fixed  charges 
at  12  per  cent.,  this  represents  an  annual  saving  of  $7,200  or  $85 
per  car.  A  study  of  the  requirements  of  this  road  showed  that 
all  cars  not  in  service  between  6  a.m.  and  midnight  could  be  housed 
by  the  small  structure  and  of  course  this  would  involve  different 
cars  on  different  days.  The  larger  car  house  and  the  increased 
annual  outlay  includes  simply  the  ability  to  house  two-thirds 
more  cars  from  midnight  until  6  a.m.  Since  the  $85  per  car  will 
nearly  provide  for  repainting  and  varnishing  a  car  each  year 
and  as  the  added  deterioration  of  the  car  during  this  period  of 
day  when  out  of  service  is  not  great,  this  particular  case  seems  to 
favor  open  storage.  Opposed  to  this  evidence  probably  the  most 
important  argument  for  complete  car  storage  is  the  fact  that  the 
equipment  will  certainly  receive  better  attention  from  inspectors 
and  repair  crew  if  all  cars  are  stored  within  the  car  house,  especi- 
ally in  bad  weather. 

The  next  question  of  importance  is  whether  a  single  or  double- 
end  house  is  desired.  The  latter  type  provides  more  ready 
movement  of  cars  through  the  house  and  aids  greatly  in  clearing 
the  house  in  case  of  fire.  Where  a  whole  block  or  two  inter- 
secting streets  are  available  it  is  often  customary  to  form  an 
operating  loop  through  the  car  house  for  the  cars  when  in  regular 
service  with  regular  inspections  as  they  stop  over  the  inspection 
pits.  A  rather  complicated  example  of  this  construction  is 
shown  in  the  plan  view  of  Fig.  119,  representing  the  new  Park 
Terminal  car  house  in  Baltimore.     The  principal  objections  to 


CAR   HOUSE    DESIGN. 


279 


the  double-end  arrangement  are  the  difficulty  in  keeping  tracks 
clear  for  thi-ough  operation,  the  large  amount  of  special  track 
work  required  and  the  added  difficulty  in  heating. 

^\^lichever  of  the  above  designs  is  decided  upon,  depending 
largely  upon  local  conditions,  the  problem  remains  to  so  connect 
the  various  tracks  of  the  car  house  with  those  of  the  main  line 
that  the  greatest  possible  flexibility  of  car  movements  within  the 
yard  may  be  had  without  interference  with  main  line  traffic  and 
without  obstructing  the  main  track  with  more  special  work  than 


Fig.  iiq. 


is  absolutely  necessary.  Figs.  120  and  121  illustrate  several 
typical  methods  of  solution  for  this  problem.  Case  (A)  introduces 
several  switches  into  one  of  the  main  tracks,  but  makes  no  con- 
nection with  the  second  main  track.  A  more  flexible  arrange- 
ment is  shown  in  Case  (B)  where  a  cross-over  is  provided  to  the 
second  main  track  in  addition  to  one  located  in  the  car  house. 
The  latter  is  often  found  very  useful,  but  its  installation  depends 
very  much  upon  the  availability  of  the  special  work  in  front  of  the 
car  house  for  switching  purposes.  If  the  special  work  in  the 
main  line  be  objected  to,  Case  (C)  may  offer  a  satisfactoiy  solu- 


28o 


ELECTRIC    RAILWAY   ENGINEERING. 


tion,  requiring  necessarily  more  yard  room.  The  design  of  Case 
(D)  uses  an  extra  or  "gauntlet"  track  in  the  street  for  switching, 
while  (E)  is  similar  to  (B)  with  the  exception  that  the  operating 
tracks  are  on  the  right  of  the  storage  house.  If  space  will  permit, 
(F)  Fig.  12  2,  offers  an  ideal  arrangement,  allowing  the  through 
cars  to  pass  through  the  car  house  for  inspection  or  minor  repairs 


Fig.   120. 


if  desired  and  relieving  the  main  line  of  all  special  work.  It  may 
also  be  used  as  a  "  Y"  for  turning  cars  which  must  operate  single- 
ended.  Designs  (G)  and  (J)  have  been  termed  "bottle"  en- 
trances involving  the  special  work  within  the  car  house  because 
of  building  conditions.  (H)  may  be  used  often  in  interurban 
service  where  land  is  cheap  and  the  car  house  may  be  placed  at 


CAR    HOUSE    DESIGN. 


281 


some  distance  from  the  main  track.  Case  (I)  involves  the  use 
of  the  third  track  in  the  street  and  therefore  is  limited  to  use 
with  wide  streets  only. 

The  special  work  required  for  any  of  the  above  entrances 
should  be  of  girder  rail  with  manganese  hardened  centers 
regardless  of  the  type  of  rail  used  in  the  street  and  car  house. 


Fk;.   121. 

This  is  especially  true  in  cases  in  which  the  regular  street  traffic 
must  pass  over  the  switches  and  frogs  as  well  as  the  cars  entering 
the  car  house. 

Transfer  Table. — The  use  of  a  transfer  table  in  the  car  house 
often  does  away  with  much  of  the  special  work.  This  transfer 
table  consists  of  a  large  truck  operating  upon  a  pair  of  depressed 


282 


ELECTRIC    RAILWAY   ENGINEERING. 


rails  laid  across  the  car  house  with  its  upper  surface  flush  with 
the  floor  and  bearing  sections  of  rail  matching  those  of  storage 
house  and  outgoing  tracks.  A  car  may  be  run  on  this  table  in 
either  direction,  be  transported  transversely  of  the  car  house  and 
run  off  on  another  track.  The  table  may  be  operated  by  hand  in 
small  installations,  but  is  ordinarily  driven  by  an  electric  motor. 
A  typical  installation  may  be  seen  in  Fig.  122.  Although  the 
transfer  table  may  be  found  in  many  city  car  houses,  it  is  seri- 
ously objected  to  by  many  because  of  the  time  required  to  shift 
cars,  especially  in  case  of  fire,  and  the  space  taken  up  thereby. 


Fig.  122. 


which  might  otherwise  be  available  for  storage.  To  obviate  these 
objections  the  "flush"  transfer  table  is  used  to  some  extent,  the 
cars  being  run  up  to  the  table  on  a  slight  gradient,  the  table 
trucks  operating  on  a  transverse  track  flush  with  the  flooi. 

Building  Design. — With  the  above  questions  determined  the 
design  of  a  suitable  building  for  a  car  house  is  a  relatively  simple 
matter.  The  two  factors  to  be  kept  constantly  in  mind  are  ease 
of  handling  and  repairing  cars  and  fire  protection. 

Fire  Protection. — Car  houses  are  recognized  to  be  consider- 
able of  a  fire  risk  and  many  serious  fires  have  consumed  many 


CAR   HOUSE    DESIGN.  283 

thousand  dollars'  worth  of  rolling  stock  in  a  surprisingly  short 
time,  the  entire  duration  of  several  such  fires  being  barely 
more  than  30  minutes.  In  many  instances  where  there  is  a 
spacious  yard  room  outside,  the  house  rails  are  stoped  toward  the 
entrance  so  that  the  cars  will  coast  out  of  the  barn  if  brakes 
are  released.  In  other  cases  many  cars  have  been  saved  in  case 
of  fire  by  throwing  the  controller  handle  to  the  first  notch  and 
allowing  them  to  run  out  without  attendance. 

Not  more  than  three  tracks  should  be  enclosed  without  a  fire- 
proof partition  and  a  single  fire-proof  section  should  not  contain 
more  than  $200,000  worth  of  rolling  stock  as  stipulated  by  the 
Fire  Underwriters.  The  best  design  is  either  brick  walls  with 
heavy  mill  type  roof  construction  of  fire-proofed  timber  or  rein 
forced  concrete  throughout.  For  the  latter  construction  see  Fig. 
122.  Steel  truss  roof  construction  has  proven  very  dangerous 
in  cases  of  fire  as  the  roof  falls  in  very  quickly,  thus  cutting  off 
all  possibility  of  getting  out  the  remaining  cars.  Curtain  walls 
of  cement  plaster  on  wire  lath  are  often  installed  in  long  houses, 
separating  the  storage  space  into  several  fire-proof  compartments. 
The  front  of  the  house  and  these  curtain  walls  are  provided  with 
steel  rolling  doors.  Opinion  is  divided  regarding  the  advantages 
of  timber  roof  trusses  over  posts  for  roof  supports.  The  latter 
of  course  obstiuct  the  working  area  somewhat,  but  are  often  used 
to  advantage  for  lighting  outlets,  sprinklers  and  the  convenient 
support  of  fire  fighting  eciuipment.  Automatic  sprinkler  systems 
are  now  being  rapidly  installed  on  ceilings  and  in  aisles  between 
cars  for  additional  and  prompt  fire  protection.  These  are  sup- 
plied with  sufficient  head  of  water  either  from  the  city  high  pres- 
sure system  or  from  a  tank  especially  installed  upon  the  premises. 
The  appearance  and  relative  dimensions  of  a  typical  car  house 
elevation  may  be  noted  in  Fig.  123. 

Pit  Construction. — For  convenience  in  inspection  and  repair, 
from  30  to  50  per  cent,  of  the  tracks  in  the  car  house  are  pit  tracks, 
i.e.,  the  floor  between  the  rails  is  depressed  several  feet  and 
cemented  as  shown  in  Fig.  123  in  order  that  the  under  portion 
of  the  car  may  be  accessible.  It  has  also  been  found  convenient 
to  depress  a  portion  of  the  floor  between  adjacent  tracks  by  one 
or  two  feet  for  convenience  in  packing  journal  boxes,  etc. 


284 


ELECTRIC   RAILWAY   ENGINEERING. 


Heating. — Car  houses  are  heated  principally  by  either  steam 
or  hot  water,  coiled  pipes  being  located  in  pits  and  upon  the 
lower  portion  of  all  walls.  The  boiler  room,  if  not  in  a  separate 
building,  must  be  carefully  protected  by  fire-proof  walls.  The 
heating  of  car  houses  is  at  best,  an  unsatisfactor}-  problem, 
especially  in  cases  where  the  end  doors  must  be  continually  open 
for  the  operation  of  cars. 

Floors. — The  floors  in  small  storage  car  houses  are  sometimes 

^of  gravel  fill.     This  is  not  to  be  approved,  however,  on  account 

of  the  impossibility  of  keeping  such  a  floor  in  a  sanitary  condition. 

Heavy  timber  flooring  is  probably  most  often  found,  but  it  should 


Fig.   i: 


be  avoided  if  the  expense  of  concrete  with  cement  finish  can  be 
seriously  considered.  Often  the  latter  can  be  constructed  with 
cinders  from  the  power  station  without  great  expense  and  will 
prove  the  most  satisfactory  of  all  car  house  floors.  Since  sub- 
stantial piers  must  be  laid  for  the  track  foundations  in  whichever 
form  it  may  take,  the  floor  is  generally  supported  therefrom. 

Lighting. — Incandescent  lighting  by  means  of  five  light  series 
groups  of  lamps  connected  between  trolley  and  ground  is  often 
used  in  smaller  installations,  but  a  low  voltage  ungrounded  supply 
is  much  preferable.  Lights  spaced  every  car  length  in  aisles 
are  usually  sufficient  for  general  illumination  if  generous  provision 
be  made  for  pit  lighting  and  outlets  for  portable  lamps.  Pit 
lighting  particularly  should  be  in  conduit  as  illustrated  in  Fig. 
124.     General  illumination  for  very  large  areas  and  for  storage 


CAR   HOUSE    DESIGX. 


28! 


yards  may  be  furnished  by  means  of  arc  lamps,  but  these  are  not 
popular  for  car  house  installation. 

Offices  and  Employee's  Quarters. — The  arrangement  of 
offices,  employee's  quarters  and  storage  for  raw  materials  and 
tools  are  dependent  upon  local  requirements  and  will  not  be  dis- 
cussed in  detail.  The  portion  of  the  building  containing  the 
offices  and  employee's  quarters  is  often  of  two  stories  and,  where 
within  the  city  limits,  is  designed  to  present  a  good  architectural 
appearance.     Many  companies  fit  up  spacious  apartments  for 


Fig.  124. 


the  use  of  employees  rather  elaborately  with  recreation  and 
reading  rooms,  sleeping  quarters,  baths,  etc.  Provision  should  at 
least  be  made  however  for  making  out  reports  and  for  comfortably 
spending  spare  time  between  "reliefs."  An  average  plan  may  be 
seen  in  Fig.  125. 

Repair  Shops. — It  is  necessary  to  decide  at  first  what  the 
policy  of  the  company  is  to  be  with  regard  to  car  repair  and  re- 
construction. If  a  large  interurban  company  is  to  make  all  re- 
pairs, reconstruct  damaged  cars  and  possibly  build  new  cars,  a 
very  elaborate  series  of  forge,  wood  working,  machine  and  paint 
shops  will  be  necessary.     The  majority  of  the  smaller  companies, 


286 


ELECTRIC    RAILWAY    ENGINEERING. 


however,  make  only  minor  repairs,  often  sending  away  wheels 
for  replacement  or  returning  rather  than  install  the  lathes  and 
hydraulic  presses  necessary  for  this  work.  Whereas  the  dis- 
cussion of  the  former  type  of  shop  is  beyond  the  scope  of  this 
treatise,  especially  as  comparatively  few  of  the  roads  are  thus 
ec[uipped,  the  following  average  list  may  be  of  value  in  planning 
the  equipment  for  a  small  shop.     The  machines  are  listed  approxi- 


Man  Hole 
3rd  Ave.  i  10th  St. 


Fig.  125. 


mately  in  the  order  in  which  they  would  be  added  with  increased 
demands  upon  the  repair  shops. 

I   Screw-cutting  lathe,  14  in.  swing. 

I  Vertical  drill  press,  24  in. 

1  Tool  grinding  wheel. 

4  Armature  stands  for  rewinding  armatures. 

2  Forges. 


CAR   HOUSE    DESIGN.  287 

I  Automatic  power  hack  saw. 

I   Oven  for  baking  insiUation. 

I   Commutator  slotting  device. 

I  Wheel  turning  lathe. 

I  Hydraulic  wheel  press. 

Whereas  the  small  repair  shop  as  well  as  the  paint  shop  often 
occupy  sections  of  the  main  car  house,  the  large  shops  are  housed 
in  separate  but  adjacent  buildings.  Such  an  arrangement, 
showing  typical  floor  plan  details,  will  be  found  in  Fig.  125. 


CHAPTER  VII. 
Electric  Locomotives. 

With  the  recent  rapid  advance  in  electric  traction  there  has 
come  the  successful  design,  construction,  and  operation  of  several 
types  of  electric  locomotives.  While  the  Baltimore  and  Ohio 
Railroad  had  previously  operated  electric  locomotives  in  its 
tunnels  for  several  years,  the  great  impetus  in  electric  locomotive 
development  came  in  1903  as  a  result  of  the  requirement  that 
the  tunnels  entering  New  York  city  be  electrified.  This  was  done 
largely  as  a  safety  precaution  soon  after  a  serious  wreck  in  one 
of  these  tunnels  due  to  the  inability  to  read  signals  on  account  of 
the  smoke  inclosed  in  the  tunnel.  Likewise  with  the  Cascade 
Tunnel  of  the  Great  Northern  Railroad  in  Washington,  experi- 
ence with  a  train  which  parted  in  attempting  to  mount  the  severe 
grade  of  the  tunnel  with  two  steam  locomotives,  resulting  in  a 
delay  of  the  train  in  the  tunnel  and  the  consequent  overcoming, 
by  poisonous  gases  and  smoke,  of  the  train  crew  and  many 
passengers,  led  to  the  recent  equipment  of  this  section  of  the  road 
with  electric  locomotives. 

With  the  multiple  unit  control  of  motor  cars,  which  has  been 
previously  described,  developed  to  such  an  extent  that  long 
heavy  trains  of  both  motor  cars  and  trailers  are  being  operated 
successfully  in  elevated,  subway  and  interuban  service,  offering  a 
very  flexible  distribution  of  motive  power  and  weight  on  driving 
wheels  throughout  the  train,  it  might  be  expected  that  this  method 
of  propulsion  would  be  applied  to  the  heavier  electrification  of 
steam  roads.  As  the  traffic  demands  and  the  number  of  cars  in- 
creased, motor  and  trail  cars  could  then  be  added  in  the  proper 
proportion  so  as  to  leave  little  excess  capacity  to  operate  at  low 
elhciency  as  must  often  be  the  case  with  but  one  or  two  capacities 
of  locomotives  used  for  trains  of  widely  varying  weights  and  re- 
quirements. 

In  spite  of  these  advantages  of  the  motor  car,  the  locomotive 


ELFXTRIC    LOCOMOTIVES.  289 

is  still  found  to  be  necessary  in  heavy  trunk  line  service.  Its 
advantages  listed  below  can  be  made  to  overcome  those  of  the 
motor  car  by  dividing  the  service  into  three  or  four  classes  such 
as  switching,  suburban,  express,  passenger  and  heavy  freight 
and  designing  different  locomotives  if  necessary  for  two  or  more 
of  these  types  of  service,  thus  keeping  the  locomotive  loaded 
approximately  to  its  rated  capacity.  The  advantages  of  the 
locomotive  in  heavy  service  may  be  listed  as  follows : 

1.  It  eliminates  necessity  of  re-equipping  present  cars  as  motor 
cars. 

2.  It  eliminates  necessity  of  wiring  some  of  the  present  cars 
with  train  cables  for  use  as  electric  trailers. 

3.  Ease  in  making  up  trains  regardless  of  whether  they  have 
been  electrically  equipped  or  not — i.e.,  the  electric  locomotive 
makes  use  of  present  cars  without  change  therein. 

4.  Not  necessary  to  make  up  trains  in  certain  order  with  proper 
number  and  location  of  motor  cars  therein. 

5.  Ease  in  reaching  parts  in  locomotive  for  repair. 

6.  Make  up  of  train  not  affected  by  failure  of  electrical  equip- 
ment. Locomotive  only  and  not  several  cars  of  train  must  be 
switched  in  case  of  electrical  breakdown. 

Granted  that  an  electric  locomotive  is  needed  if  trunk  line 
service  is  to  be  electrified,  a  study  of  the  various  types  of  electric 
locomotives  which  are  in  use  at  the  present  time  is  of  interest. 
With  the  many  years  of  experimenting  and  practical  experience 
with  steam  locomotives  which  have  led  to  a  most  satisfactory 
design  for  the  various  types  of  service,  advantage  was  taken  of 
present  steam  locomotive  design,  and  the  electrical  equipment 
added  with  as  little  change  as  possible.  To  this  end  the  man- 
ufacturers of  steam  locomotives  and  electrical  machinery  have 
cooperated  to  a  marked  degree  in  developing  the  new  product. 

In  the  early  locomotives  it  was  believed  to  be  necessary,  however, 
to  mount  the  motors  on  the  driving  axles  between  drivers  as  in 
the  case  of  motor  cars  with  consecjucnt  limitation  in  capacity 
of  motors  if  the  present  gauge  of  track  and  short  wheel  base  are  to 
be  retained.  The  change  of  track  gauge  was  of  course  practically 
impossible  with  the  present  installation  of  standard  gauge  roads 
in  the  country  and  an  increase  in  the  length  of  wheel  base  in- 
19 


290 


ELECTRIC    RAILWAY    ENGINEERING. 


troduced  difficulties  in  rounding  curves.  In  fact,  any  limitation 
upon  the  flexibility  of  the  truck  and  the  free  and  independent 
vertical  and  transverse  movement  of  individual  axles  with  ir- 
regularities in  the  track  tends  to  move  the  entire  mass  of  the  loco- 
motive, thus  introducing  bad  riding  qualities  and  vibrations  which 


Fic.   ij6. 


Fig.  127. 


become  dangerous  at  high  speeds.  An  attempt  was  first  made, 
therefore,  to  vary  the  design  of  the  large  interurban  motors  to 
crain  greater  capacity  upon  the  limited  size  of  trucks  and  later 
to  remove  the  motor  from  the  truck  axles,  as  will  be  shown 
below. 

The  New  York  Central  locomotive,  Fig.  126,  of  the  direct  cur- 


ELECTRIC    LOCOMOTIVES. 


291 


rent  type,  a  plan  view  of  whose  motor  is  shown  in  Fig.  127, 
marked  a  radical  departure  in  railway  motor  design.  As  will  be 
noted  from  the  figure,  the  motor  is  bipolar,  the  magnetic 
circuit  involving  a  portion  of  the  truck  frame  with  internally 
projecting  laminated  iron  poles  with  \-ertical  faces,  between  which 
the  armature,  mounted  directly  on  the  truck  axle,  might  ^•ibrate 
in  a  vertical  direction  with  the  irregularities  in  the  track.     This 


ri  ■;■  ker 


Fig.  128. 


design,  of. course,  considerably  increased  the  capacity  possible  in 
the  limited  space  on  the  truck,  eliminated  many  of  the  disad- 
vantages of  the  small  air  gap  and  gave  considerable  flexibility 
to  the  relative  movement  of  armature  and  field.  It  also  lowered 
the  center  of  gravity  of  the  locomotive  below  that  of  its  steam 
railroad  competitor  and  increased  the  dead  load  per  axle,  both 
of  which  changes  have  been  considered  as  disadvantages  by 
some  engineers. 

The  locomotives  of  the  New  York,  New  Haven  and  Hartford 
Railroad,  Fig.  128,  which  were  developed  soon  after  the  above 
for  operation  upon  the  11,000  volt  single-phase  system  of  the 


292 


ELECTRIC    RAILWAY   ENGINEERING. 


above  company  not  only,  but  also  upon  the  600  volt  direct-current 
system  of  the  New  York  Central  Railroad  entering  New  York 
City  still  retained  the  motors  concentric  with  the  truck  axles 
and  between  the  driving  wheels  as  will  be  seen  from  Fig.  129, 
but  reduced  the  dead  weight  upon  the  axles  by  supporting  the 
armature  upon  a  quill,  concentric  with,  but  surrounding  the 
dri\-ing  axle  with  a  space  of  5  /8  in.  between  axle  and  inner  cir- 
cumference of  quill.     The  torque  was  transmitted  from  armature 


Fig.  i2g. 


to  drivers  by  means  of  seven  driving  pins,  spring  borne  in  re- 
cesses in  the  driving  wheels  as  shown  in  Fig.  130.  This  allowed 
the  axle  considerable  motion  independent  of  the  armature  not 
only,  but  permitted  the  motor  field  and  frame  to  be  rigidly  sup- 
ported upon  the  truck. 

After  some  few  years  of  experience  with  the  operation  of  the 
above  locomotives  and  a  careful  study  of  their  characteristics  as 
compared  with  steam  locomotives,  the  principle  problem  in 
design  seemed  to  be  resolved  to  that  of  the  transmission  between 
motor  axle  and  driving  wheels.  Messrs.  Storer  and  Eaton  in  a 
recent  paper  before  the  American  Institute  of  Electrical  Engi- 


ELECTRIC    LOCOMOTIVES. 


293 


neers^  have  presented  this  problem  in  a  very  concise  form  and 
because  of  its  importance  in  electric  locomotive  design  and  as 
designing  engineers  in  both  this  country  and  abroad  are  at  vari- 
ance regarding  the  best  method  of  transmission  to  adopt,  a  state- 
ment of  the  various  types  in  use,  together  with  illustrations  of 
each  have  been  taken  from  the  above  paper  and  are  herein 
included. 


Fig.  130. 


a.  "  Gearless  motor  with  armature  pressed  onto  driving 
axle,  'New  York  Central,'  Fig.  131  a. 
Gearless   motor   with   armature   carried   on   a   quill 
surrounding   axle,    and  driving  the  wheels  through 
flexible   connections,    'New   Haven  Passenger,'   Fig. 


b. 


131  b. 


c.  "  Geared  motor  with  bearings  directly  on  axle  and  with 

nose  supported  on  spring-borne  parts  of  locomotive, 
'St.  Claire  Tunnel,'  Fig.  132  c. 

d.  "Geared  motor  with  bearings  on  a  quill  surrounding 

axle,  and  (i)  nose  supported  on  spring-borne  parts 
of  machine  (New  Haven  Car,  Fig.  132  d)  and  (2) 
motor  rigidly  bolted  to  spring-borne  parts  of  machines, 

^  The  Design  of  the  Electric  Locomotive,  by  N.  W.  Slorer  and  t}.  M.  Eaton, 
A.  I.  E.  E.,  Vol.  XXIX. 


294 


ELECTRIC    RAILWAY    ENGINEERING. 


the  quill  having  sufficient  clearance  for  axle  move- 
ments, 'Four  motor  New  Haven  Freight, '  Fig.  132  d'. 
"Motor  mounted  rigidly  on  spring-borne  parts,  arma- 


ture rotating  at  same  rate  as  drivers,  power  trans- 
mitted to  drivers  through  cranks,  connecting  rods 
and  counter  shaft  on  level  with  driver  axles.  'Penn- 
sylvania,' Fig.  133. 


ELECTRIC    LOCOMOTIVES. 


295 


f.  "  Motor  mounting  and  transmission  as  in  (e)  but  motor 
fitted  with  double  bearings  one  part  for  centering 
motor  crank  axle  and  the  other  for  centering  the 
armature  fiuill  which  surrounds  and  is  flexibly  con- 


FiG.  133. 

nected  to  the  motor  crank  axle.     'Two  motor  New 
Haven  Freight,'  Fig.  134  f. 

"Motors  mounted  on  spring-borne  parts,  armature 
rotating  at  same  rate  as  drivers,  power  transmitted 
to  drivers  through  off-set  connecting  rods  and  side 
rods.     'Latest  Simplon  Locomotives,'  Fig.  134  g- 


Fig.  134. 

h.  "Motors  mounted  on  spring-borne  parts,  armature 
rotating  at  same  rate  as  drivers,  power  transmitted 
to  drivers  through  Scotch  yokes  and  side  rods. 
'Valtellina  Locomotives,'  Fig.  134  h. 


296 


ELECTRIC    RAILWAY    ENGINEERING. 


i.  "  Motors  mounted  rigidly  on  spring-borne  parts,  power 
transmitted  through  gears  to  counter-shaft,  thence 
to  drivers  through  Scotch  yokes  and  side  rods.  Fig. 
I35-" 

It  will  be  seen  from  the  above  that  the  locomotives  of  the 
Pennsylvania  Railroad  mark  a  rather  radical  departure  from  the 
designs  previously  described,  having  their  motors  above  the 
trucks  in  the  cab  and  returning  to  the  connecting  rods  of  the 
steam  locomotives  for  transmission  to  the  drivers.  This  design 
raises  the  center  of  gravity  and  permits  practically  unlimited 


Fig.  135. 

motor  capacity  in  a  single  unit  as  its  dimensions  may  be  increased 
longitudinally  at  will  and  transversely  by  overhanging  the  driving 
wheels.  This  locomotive,  which  is  designed  in  two  sections 
which  may  operate  separately,  but  which  are  intended  for  opera- 
tion in  pairs,  is  illustrated  in  Fig.  136,  the  slanting  driving  rod 
seen  in  the  figure  connecting  with  a  single  motor  in  each  cab 
and  being  properly  balanced  by  means  of  a  counter-weighted 
crank  disc. 

Control  Systems. — While  the  details  of  the  specifications  for 
the  various  types  of  electric  locomotives  built  thus  far  in  this 
country  are  concisely  set  forth  in  Tables  XXVI  and  XXVII  below, 
an  additional  word  regarding  the  systems  of  control  used  may 
be  of  interest. 

The  New  York  Central  locomotives  having  four  550  H.  P., 
600  volt  direct  current  motors  each  operating  upon  a  third  rail 
distribution     system     have     three     running    steps     on     their 


ELECTRIC    LOCOMOTIVES. 


297 


controllers,  the  first  with  all  motors  in  series,  the  second  consist- 
ing of  two  groups  in  parallel  series  and  finally  all  motors  in  series. 
The  control  is  of  the  multiple  unit  type  similar  to  that  previously 
described  for  motor  cars  with  a  master  controller  and  train  cable 
with  coupling  plugs  so  that  two  or  more  locomotives  may  be 
operated  together  from  a  single  engineer's  cab. 


Fig.   i;6. 


The  New  York,  New  Haven  and  Hartford  control  equipment 
is  the  A.  C.  D.  C.  unit  switch  control  operating  two  motors  per- 
manently in  series.  Upon  the  direct  current  system  of  the  New 
York  Central  terminal  system  the  series-parallel  control  is  used 
and  upon  the  high  voltage  alternating  current  section  the  auto- 
transforrrier  steps  the  voltage  down  to  si.x  different  values  each  of 
which  is  a  permanent  running  voltage.  About  double  this 
number  of  steps  are  rcf^uired  for  smooth  acceleration  upon 
direct  current,  but  because  of  the  motor  design  used  these  extra 
steps  may  be  secured  in  the  series  position  by  shunting  the  fields. 
This  may  be  done  in  steps  until  the  fields  are  at  about  one-half 


298  ELECTRIC    RAILWAY    ENGINEERING. 

their  nominal  flux  rating  without  interfering  with  their  successful 
operation.  Each  locomotive  is  equipped  with  four  250  H.  P. 
motors  nominal  capacity,  which  are  capable  of  exerting  200  H.  P. 
each  continuously.  A  pair  of  motors  require  450  volts  alternat- 
ing current  and  600  volts  direct  current  for  full  rated  speed. 

Each  section  of  the  Pennsylvania  locomotives  contains  a  single 
motor  rated  at  2000  H.  P.  It  is  of  the  interpole  (10  pole)  type 
designed  for  use  upon  600  volts  direct  current.  The  motors 
are  controlled  by  the  unit  switch  electro-pneumatic  master  con- 
trol system  previously  described,  having  four  running  notches  as 
follows : 

1.  Series  connection  with  full  field, 

2.  Series  connection  with  normal  field, 

3.  Parallel  connection  with  full  field, 

4.  Parallel  connection  with  normal  field. 

These  locomotives  are  provided  with  both  third  rail  shoes  and 
trolleys  for  either  type  of  current  collection. 

As  has  been  previously  stated  the  locomotives  of  the  Cascade 
Tunnel  Division  of  the  Great  Northern  Railroad  are  the  only 
examples  of  polyphase  traction  in  this  country.  In  this  par- 
ticular case  the  installation  of  a  motor  with  inherent  constant 
speed  characteristics  seemed  advisable  where  long  runs  over 
practically  constant  high  grades  at  relatively  low  speeds  were 
demanded.  The  control  of  the  three-phase  motors  of  these 
locomotives  is  similar  to  that  for  the  variable  speed  slip-ring  type, 
phase  wound  rotor  induction  motors  used  in  stationary  service. 
It  consists  in  inserting  resistances  in  series  with  the  tliree  phases 
of  the  rotor  winding  and  gradually  cutting  out  these  resistances 
in  one  phase  after  another  by  means  of  a  controller.  By  thus 
varying  the  resistance  of  but  one  phase  at  a  time  more  accelerat- 
ing points  are  obtained  with  less  complicated  wiring  than  when 
all  three  phases  are  changed  simultaneously.  This  is  done, 
however,  at  the  expense  of  unbalanced  currents  in  the  motor  and 
would  not  therefore  be  advisable  under  frequent  starting  condi- 
tions. The  motors  are  of  eight  poles  each,  designed  for  a  fre- 
quency of  25  cycles  and  employ  forced  ventilation  for  cooling. 
The  voltage  is  reduced  by  transformers  on  the  car  from  6600  to 


ELECTRIC    LOCOMOTIVES. 


299 


500  volts.  A  speed  of  approximately  15  m.  p.  h.  is  maintained 
in  both  directions  upon  an  average  and  fairly  constant  grade  of 
1.7  per  cent. 

Data  on  Electric  Locomotives. — The  following  tables  taken 
from  a  paper  by  Westinghouse  on  "The  Electrification  of  Rail- 
ways" presented  before  the  joint  meeting  of  the  American 
Society  of  Mechanical  Engineers  and  the  Institution  of  Mechan- 
ical Engineers  in  London  in  1910  represent  very  concisely  the 
details  of  design  of  American  electric  locomotives. 


TABLE  XXVI. 
Data  on  Westinghouse  Electric  Locomotives. 


Grand 

Built  for 

New 

Trunk 

Pennsyl- 

New 

New 

Haven 

St.  Clair 

vania 

Haven 

Haven 

Tunnel 

Electric  system 

A.  C.D.C. 

A.  C 

D.  C 

A.  C.  D.  C. 

A.  C.  D.  C. 

Service 

Passenger 

Frt.  &  Pass. 

Passenger. 

Frt.  &  Pass. 

Frt.  &  Pass 

First  placed  in  service 

July  1907 

Feb.  1908. . 

17,000- 
mile  test. 

3,000-mile 

test. 

Building. 

No.  in  service  or  on  order, 

41 

6 

24 

I 

I 

May,  1910. 

No.  motors  per  locomotive. 

4 

3 

2 

4 

2 

Armature  diameter,  inches  . 

39i 

30 

56 

39i 

76 

Core  length,  including  vent. 

18 

i4i 

23 

13 

13 

opening,  inches. 

Weight  I  motor,  pounds. . . . 

16,420 

15,660 

45.000 

19.770 

41,600 

Wt.  all  motors  on  locomotive 

65,680 

46,980 

90,000 

79,080 

83,200 

Wt.  all  electrical  parts 

1 10,400 

58,400 

127,200 

130,000 

135,000 

Wt.  all  mechanical  parts .  .  . 

94,100 

73,600 

204,800 

130,000 

125,000 

Wt.  complete  locomotive.  .  . 

204,500 

132,000 

332,000 

260,000 

260,000 

Wt.  on  driving  wheels 

162,000 

132,000 

207,800 

180,000 

180,000 

Wt.    complete    locomotive 

196,000 

132,000 

D.  C 

241,000 

240,000 

for  A.  C.  operation. 

Max.  guar't'd  speed  m.p.h. 

About  86 

30 

.\bout  80 

45 

45 

Feature  limiting  speed 

Track. . .  . 

Armature... 

Connecting 
rod. 

Armature.  . 

Armature. 

Max.  tractive  effort 

19,200 

43,800 

69,300 

40,000 

40,000 

Loco.  wt.  in  excess  of  i8% 

88,700 

None 

None 

18,500 

17.500 

adhesion  Max.  T.  E.,  A.  C. 

operation. 

Designed  for  trailing  load. 

250 

500 

550 

r  1500  frt. 

/  1500  frt. 

tons. 

[    800  pass. 

\    800  pass. 

Balance  speed  on  level  with 

About  75 

About    25 

60 

35  frt. 

3  5  fit. 

above  load. 

45  pass. 

45  pass. 

JOO 


ELECTRIC    RAILWAY   ENGINEERING. 


TABLE  XXVII. 
Data  on  General  Electric  Locomotives. 


Built  for 

N.  Y.  C. 

& 
H.  R.  R. 

Detroit 
River 
Tunnel 

B.  &0.  R.R 

Great 
Northern 

Paris- 
Orleans 

D.  C 

D.  C 

D.  C 

3 -phase. . 

D.  C. 

Passenger 
July  1906 

Frt.  &  Pass. 
Tests  com- 

Frt. &  Pass. 
March  19 10 

Frt.  &  Pass. 
July  1909   . 

Passenger. 

First  placed  in  service 

1899 

pleted. 

No.  in  service  or  on  order 

47 

6 

2 

4 

II 

May,  1910. 

No.  motors  per  locomotive. 

4 

4 

4 

4 

4 

Armature  diameter,  inches. 

29 

2S 

25 

3Sf 

23i 

Core  length,  including  vent. 

19 

11'^ 

Hi 

i6i 

12 

opening,  inches. 

Wt.  one  motor,  pounds 

18,150 

10,560 

10,560 

15,000 

8,855 

Wt.  all  motors  on  locomotive 

72,600 

42,240 

42,240 

6o,oco 

35.420 

"Wt.  all  electrical  parts 

91,200 

54,000 

54,000 

109,000 

42,500 

Wt.  all  mechanical  parts .  .  . 

138,800 

146,000 

130,000 

121,000 

67.500 

Wt.  complete  locomotive. . . 

230,000 

200,000 

184,000 

230,000 

110,000 

Wt.  on  driving  wheels 

141,000 

200,000 

184,000 

230,000 

1 10,000 

Wt.     complete    locomotive 

D.C 

D.  C 

D.  C 

230,000 

D.  C. 

for  A.  C.  operation. 

Max.  guar't'd  speed,  m.p.h. 

75 

30 

55 

30 

45 

Feature  limiting  speed 

Track  .  .  . 

,\rmature.. 

Armature.  . 

Armature.  . 

Armature. 

Max.  tractive  effort 

47,000 

67,000 

61,000 

77,000 

37,000 

Loco.  wt.  in  excess  of  i89( 

None. .  .  . 

None 

None 

None 

None. 

adhesion  Max.  T.  E.,  A.  C. 

operation. 

Designed  for  trailing  load. 

850  on  ii% 

600     grade. 

500    grade. 

2 . 2  %  grade 

Balance  speed  on  level  with 

45 

Frt.      20.5 

Frt.     26 

IS 

300 

63 

Pass.   22 

Pass.  30 

32 

Although  some  arguments  in  favor  of  the  electric  locomotive 
as  compared  with  its  steam  rival  will  be  considered  in  a  later 
chapter,  it  may  be  said  in  the  conclusion  of  this  discussion  that 
the  electric  locomotive  has  accomplished  thus  far  all  that  has 
been  required  of  it,  i.e.,  to  operate  as  satisfactorily  as  the  steam 
locomotive  under  all  conditions  of  service  and  eliminate  the 
disadvantages  coincident  with  smoke  and  dirt  of  the  latter.  It 
has  also  shown  itself  capable  of  accelerating  more  rapidly  than 
its  competitor,  which  particularly  commends  it  where  headway 
is  short  and  stops  are  frequent.  It  can  readily  be  designed  for 
a  draw  bar  pull  considerably  in  excess  of  that  of  the  largest  steam 
locomotives.     It  has  therefore  found  a  permanent  place  in  the 


ELECTRIC    LOCOMOTIVES.  30I 

electrification  of  terminals  and  its  future  now  seems  to  be  one  of 
further  adaptation  and  adoption,  although  its  depreciation  and 
maintenance  in  comparison  with  the  steam  locomotive  can  hardly 
be  intelligently  compared  at  present. 

Gasolene  Electric  Car. — Although  not  strictly  confined  to  the 
function  of  a  locomotive,  the  gasolene  electric  car  should  be  given 


Fig.   137. 

a  place  in  the  discussion  of  electric  traction.  In  several  instances, 
particularly  upon  small  branch  roads  acting  as  feeders  to  trunk 
lines,  where  traffic  is  light  and  the  installation  of  an  electrical 
distribution  system  therefore  unwarranted,  and  yet  where  the 
advantages  of  electric  traction  are  worthy  of  serious  considera- 
tion, the  gasolene  electric  car  has  found  a  place.  This  car  not 
only  provides  for  from  40  to   50  passengers,   together  with  a 


Fig.   i,^S. 


baggage  compartment,  but  also  is  a  complete  power  plant,  a 
flexible  distribution  system  and  a  motor  car  combined.  In  the 
front  end,  above  the  floor,  is  located  an  eight  cylinder,  100/125 
H.  P.  four-cycle-gasolene  engine,  direct  connected  to  an  80  K.  W., 
600  volt  commutating  pole  direct  current  generator  with  exciter. 
A  series  i)arallel  controller  regulates  the  supply  of  current  from 


302  ELECTRIC    RAILWAY    ENGINEERING. 

this  generator  to  two  loo  H.  P.  motors  mounted  on  the  front 
trucks.  Additional  flexibility  of  control  is  provided  by  the 
regulation  of  the  voltage  supplied  to  the  motors  by  the  variation 
of  the  generator  field  strength.  The  controller  is  also  provided 
with  means  for  regulating  the  engine  ignition  and  the  throttle. 
The  car  may  be  started,  stopped,  and  reversed  with  the  engine 
running  continuously  in  one  direction.  A  trolley  is  often  pro- 
vided by  means  of  which  the  car  may  be  operated  on  standard 
direct  current  trolley  systems  without  change  in  the  control 
equipment. 

Reports  from  roads  where  these  cars  have  been  installed  show 
a  marked  reduction  in  operating  expenses  and  maintenance 
charges  over  those  of  steam  operated  trains,  although  their  com- 
paratively recent  introduction  has  not  permitted  an  accurate 
comparison  over  an  extended  period.  A  plan  and  elevation  of 
one  of  these  cars  may  be  found  in  Figs.  137  and  138  respectively. 


PART  IV. 

TYPES  OF  SYSTEMS. 


CHx\PTER  I. 
/Vlterxatixg  Current  vs.  Direct  Current  Traction. 

The  problem  to  be  discussed  under  the  above  caption  is  one 
that  has  received  much  attention  during  the  past  few  years  bv 
steam  and  electric  railroad  officials,  consulting  engineers  and 
electrical  manufacturing  companies.  It  has  been  the  target  of 
much  discussion  before  technical  societies  and  in  the  technical 
press,  at  times  involving  rather  heated  criticisms  based  upon 
both  accurate  engineering  data  and  the  enthusiastic  prophecies 
of  more  or  less  prejudiced  engineers.  To  sift  out  the  salient 
factors  in  the  case  and  outline  the  present  status  of  the  problem 
in  a  few  words  becomes,  therefore,  a  difificult  task. 

Whereas  the  greater  part  of  the  discussion  of  this  subject  has 
been  in  connection  with  the  electrification  of  steam  roads,  because 
of  the  prominence  of  the  latter  problem  at  the  present  time,  before 
which  the  selection  of  a  motive  power  for  an  interurban  svstem 
immediately  becomes  dwarfed  in  magnitude,  yet  the  consideration 
of  this  latter  subject  has  purposely  been  made  to  precede  that  of 
"Electric  Traction  on  Trunk  Lines"  because  of  its  broader 
applicability  to  interurban  systems,  steam  railroad  electrification 
and  possibly  to  city  traction  systems  under  some  peculiar  local 
conditions. 

The  systems  which  have  sufficient  advantages  and  for  which 
complete  power  station,  distribution  and  rolling  stock  equipment 
have  been  sufficiently  de\eIoped  to  warrant  consideration  in  this 
problem  are  the  following. 

1.  Polyphase  system, 

2.  Direct  current  600  volt  system, 

3.  Direct  current  1200  volt  system, 

4.  Single  phase  high  voltage  system. 

The  polyphase  system,   although  least  important,   has  been 
considered  first  for  the  reason  that  it  may  be  readily  classed 
separately  and  therefore  omitted  from  the  more  detailed  com- 
20  305 


3o6  ELECTRIC    RAILWAY   ENGINEERING. 

parison  which  follows.  The  following  characteristics  of  the 
polyphase  system  prevent  its  selection  except  for  very  special 
cases  in  which  speeds  may  be  low  and  constant,  stops  infrequent, 
service  and  grades  heavy  and  fairly  constant  and  operation  with 
relatively  low  efficiency  and  complicated  control  not  objection- 
able. 

a.  Constant  speed  characteristics, 

b.  Only  the  one-half  and  full  speed  operation  efficient, 

c.  Control  equipment  complicated, 

d.  Unbalanced  motor  currents  during  acceleration, 

e.  Complicated  distribution  system  involving  either  three 
trolley  wires  and  three  trolleys  per  car  or  two  of  each  of  the  above 
with  a  track  return  for  the  third  phase, 

f.  Cannot  be  operated  upon  direct  current. 

With  the  above  explanation  of  the  peculiar  conditions  under 
which  the  polyphase  system  must  operate,  which  has  thus  far 
limited  its  installation  to  a  single  road  in  this  country  which  has 
been  previously  described  herein,  the  remaining  three  systems 
will  be  compared  upon  as  nearly  the  same  basis  as  possible.  The 
peculiarities  of  each  system,  which  may  result  in  advantages  or 
disadvantages  depending  upon  local  conditions  in  each  instal- 
lation, will  be  discussed  in  connection  with  the  several  determining 
and  distinctive  functions  of  the  complete  railway  system. 

Power  Station. — The  power  station  is  not  materially  dififerent 
for  the  three  systems  for  a  long  road,  involving  as  it  does  three- 
phase  generating  equipment  and  step-up  transformers,  together 
with  the  control  of  three-phase  high  tension  transmission  Hnes. 
If  the  single  phase  system  be  operated  with  a  single-phase  gener- 
ating station,  which  is  the  exception  rather  than  the  rule,  the 
first  cost  and  size  of  generating  equipment  are  increased  for  a 
given  output,  but  the  switchboard  and  control  are  slightly 
simplified. 

Transmission  Lines. — No  material  difference  exists  between 
the  systems  in  regard  to  transmission,  so  long  as  three-phase 
transmission  is  adopted.  The  costs  of  these  lines  for  all  three 
systems  are  therefore  practically  identical.  In  the  compara- 
tively few  installations  where  single-phase  transmission  might 
be  adopted,  the  design  and  construction  of  the  line  is  simplified 


ALTERNATING    VS.    DIRECT    CURRENT    TR^VCTION  307 

by  the  use  of  two  wires  in  place  of  three,  but  for  a  given  power 
transmitted  and  a  fixed  efficiency  of  transmission  the  cost  of 
copper  in  the  three-phase  system  is  25  per  cent.  less.  This 
will  usually  more  than  balance  the  added  installation  and  main- 
tenance cost  of  the  third  wire. 

Substation. — In  the  design  of  the  substation  is  found  one  of 
the  most  marked  variations  in  the  three  systems.  As  explained 
in  a  previous  chapter  the  two  direct  current  systems  require  the 
installation  of  transformers,  synchronous  converters  or  motor 
generators  and  switchboards  in  the  substation,  whereas  the  alter- 
nating current  system  calls  for  the  transformers  and  automatic 
control  switches  only.  This  not  only  greatly  reduces  the  first  cost 
and  maintenance  in  the  latter  system,  but  eliminates  the  services 
of  an  attendant.  The  elimination  of  this  converting  equipment 
will  be  found  from  the  tables  listed  below  to  lower  the  first  cost  of 
substation  to  27  per  cent,  and  37.5  per  cent,  of  the  600  volt  and 
1200  volt  substations  respectively,  while  the  operating  costs  are 
reduced  respectively  to  26.2  per  cent,  and  58.2  per  cent,  of  the 
direct  current  substations.  This  is  not  clear  gain  on  the  part  of 
the  single-phase  system,  however,  as  it  is  partially  balanced  by 
the  increased  cost  of  rolling  stock  in  the  latter  system. 

In  the  relatively  few  instances  in  which  the  increase  in  dis- 
tribution voltage  in  the  single-phase  system  is  sufficient  to  permit 
the  economical  transmission  for  the  entire  length  of  the  line  at 
trolley  potential,  the  substation  cost  and  maintenance  is  not 
only  entirely  eliminated,  but  the  step-up  transformers  at  the 
powxr  station  may  usually  be  eliminated  as  wxll  and  the  switch- 
board considerably  simplified  in  consec{uence. 

If  the  single-phase  equipment  were  as  well  developed  and 
standardized  as  the  600  volt  direct  current  apparatus  a  lower 
depreciation  factor  might  be  applied  to  the  former  substation 
because  of  the  relatively  shorter  life  of  the  commutating  machinery 
of  the  latter  station,  but  it  is  probable  that  the  allowance  for 
obsolescence  which  must  be  made  in  the  depreciation  charges  on 
recently  developed  equipment  will  compensate  for  any  such  re- 
duction. 

The  first  cost  of  the  1200  volt  direct  current  substation  is  but 
73  per  cent,  of  the  600  volt  station  because  of  the  lower  current 


308  ELECTRIC    RAILWAY    ENGINEERING. 

value  necessary  for  the  same  output,  thereby  reducing  the  size 
and  cost  of  converters,  cables  and  switchboard. 

Distribution  System. — As  would  naturally  be  expected  the 
first  cost  of  the  distribution  system  decreases  with  increase  of 
voltage,  thereby  favoring  the  1200  volt  direct  current  and  3300  to 
1 1 ,000  volt  single  phase  systems,  especially  in  cases  where  traffic 
is  sufficiently  heavy  to  require  the  installation  of  the  third  rail 
in  case  of  the  600  volt  system.  While  this  gain  in  first  cost  is 
admitted  by  the  advocates  of  the  direct  current  system  in  case  of 
wooden  pole  line  construction  attention  is  called  to  the  fact 
that  with  so-called  "permanent"  overhead  construction,  referring 
to  the  double  catenary  supported  on  steel  bridges  with  long  spans, 
the  cost  of  the  overhead  is  quite  equal  to  that  of  the  third  rail 
construction. 

Rolling  Stock. — With  the  equipment  of  rolling  stock 
the  pendulum  of  efficiency,  lirst  cost  and  possibly  of  main- 
tenance swings  in  the  other  direction  favoring  the  direct  current 
system. 

Single-phase  motors  in  their  present  stage  of  development 
are  generally  believed  to  be  slightly  inferior  to  the  direct  current 
motor  in  efficiency  and  quick  accelerating  qualities  for  a  given 
rating.  They  are  also  considerably  heavier  for  a  given  output, 
thus  increasing  the  weight  of  car  to  be  accelerated  for  a  given 
traffic  return.  The  above  are  general  conclusions  which  will 
probably  be  conceded  by  both  factions  that  have  entered  the 
rather  extended  controversy  regarding  the  relative  advantages 
and  disadvantages  of  the  single-phase  motor  for  traction  pur- 
poses. That  this  question  is  far  from  being  decided  is  illustrated, 
however,  in  the  following  discussions  of  the  subject  before  the 
American  Institute  of  Electrical  Engineers,  which  have  been 
quoted  herein  for  the  double  purpose  of  pointing  out  the 
unsettled  condition  of  single-phase  motor  development  at  the 
present  time  as  well  as  illustrating  the  various  details  of  design 
under  question. 

Sprague  points  out  the  following  differences  between  the  single- 
phase  and  direct  current  motors.^ 

'  "Some  Facts  and  Problems  Bearing  on  Trunk  Line  Operation,"  by  Frank  J. 
Sprague,  A.  I.  E.  E.,  VoL  XXVI. 


ALTERNATING    VS.    DIRECT    CURRENT    TR.\(  TION.  309 

"i.  The  input  of  current  in  one  is  continuous;  in  the  other 
intermittent. 

"2.  One  has  a  single  frame,  the  electrical  and  mechanical  parts 
being  integral;  the  other  has  a  laminated  frame  contained  within 
an  independent  casing.  Hence  there  is  not  equal  rigidity,  or 
equal  use  of  metal. 

"3.  One  has  exposed  and  hence  freely  ventilated  ficld-coils; 
the  other  has  field-coils  imbedded  in  the  field-magnets. 

"4.  One  has  a  large  polar  clearance,  and  consec[uently  ample 
bearing-wear;  the  other  has  an  armature  clearance  of  about  only 
one-third  as  much,  and  hence  limited  bearing-wear. 

''5.  One  is  operated  with  a  high  magnetic  flux,  and  conse- 
quently high  torque  for  given  armature-conductor  current;  the 
other  has  a  weak  field,  and  consequent  lower  armature  tor([ue. 

''  6.  One  has  a  moderate  sized  armature  and  commutator,  and 
runs  at  a  moderate  speed;  the  other,  with  equal  capacity,  has  a 
much  larger  diameter  of  armature  and  commutator,  and  runs 
at  a  much  higher  speed. 

"7.  One  permits  of  a  low  gear-reduction,  and  consequently  a 
large  gear-pitch;  the  other  requires  a  higher  gear-reduction,  and 
a  weaker  gear-pitch. 

"8.  The  windings  of  one  are  subject  to  electrical  strains  of  one 
character;  in  those  of  the  other  the  strains  are  of  rapidly  variable 
and  alternating  character. 

''9.  The  mean  torque  of  one  is  the  corresponding  maximum; 
the  mean  torque  of  the  other  is  only  about  two-thirds  of  the 
maximum. 

"  10.  The  torque  of  one  is  of  continuous  character;  that  of  the 
other  is  variable  and  pulsating,  and  changes  from  nothing  to  the 
maximum  fifty  times  a  second. 

"11.  One  has  two  or  four  main  poles  only,  two  paths  only 
in  the  armature,  and  two  fixed  sets  of  brushes;  the  other  has 
four  to  fourteen  poles,  as  many  paths  in  the  armature,  lead- 
ing to  unbalancing,  and  as  many  movable  sets  of  commutator 
brushes. 

"12.  One  can  maintain  a  high  torque  for  a  considerable  time 
while  standing  still;  the  other  is  apt  to  burn  out  the  coils,  which 
are  short  circuited  under  the  brushes. 


3IO  ELECTRIC    RAILWAY   ENGINEERING. 

"  13.  In  one,  all  armature-coil  connections  are  made  directly 
to  the  commutator;  in  the  other,  on  the  larger  sizes  resistances 
are  introduced  between  the  coils  and  every  bar  of  the  commutator, 
some  of  which  are  always  in  circuit,  and  the  remainder  always 
present. 

"  14.  In  one  the  sustained  capacity  for  a  given  weight  is  within 
the  reasonable  requirements  of  construction;  in  the  other  it  is 
only  about  half  as  much. 

"15.  Finally,  the  gearless  type,  with  armature  and  field  vary- 
ing relatively  to  each  other,  is  available  for  one,  but  this  con- 
struction is  denied  to  the  other. 

"Consideration,  then,  of  the  characteristics  peculiai  to  each 
class  of  motor  indicates  not  that  the  single-phase  motor  cannot 
be  used,  but  that  if  adopted  the  weight  or  number,  and  the  cost 
of  locomotives  or  motors  required  to  do  the  work  must  be  much 
greater;  that  the  depreciation  of  that  which  is  in  motion  will  be 
much  higher;  and  that  there  will  always  be  an  excess  weight  of 
fixed  amount  per  unit  which  must  be  carried  irrespective  of  the 
trailing  or  effective  loads.  We  must,  therefore,  in  many  cases 
be  led  to  the  selection  of  the  direct-current  motor,  that  motor 
which  has  the  higher  weight  capacity,  the  greater  endurance,  and 
the  lower  cost  per  unit  of  power." 

In  discussing  this  paper  Storer  criticizes  each  point  in  turn 
as  quoted  below.  ^ 

"i.  'The  input  of  current  in  one  is  continuous;  in  the  other, 
intermittent.'  Quite  true,  but  the  draw-bar  pull  is  quite  as 
effective  in  one  case  as  in  the  other. 

"2.  The  direct-current  motor  has  a  solid  frame  like  the  single- 
phase  motor.  It  has,  further,  two  or  more  laminated  poles 
bolted  in,  and  if  the  interpole  construction  is  used  has  as  many 
more  relatively  small  and  delicate  poles.  The  alternating-cur- 
rent motor  as  built  .by  the  company  with  which  I  am  connected 
has,  in  all  sizes  up  to  a  diameter  of  38  in.  field  punchings  made 
in  a  single  piece  and  built  up  and  keyed  in  the  frame,  making 
it  as  solid  a  construction  as  an  armature  on  its  spider.  The 
claim  for  less  rigidity  in  the  single-phase  motor  is,  therefore,  not 
sustained. 

'Discussion  of  above  paper  by  N.  W.  Storer,  A.  I.  E.  E.  Vol.  XXVI. 


ALTERNATING    VS.    DIRECT    CURRENT    TR.VCTION.  3II 

"3.  'One  has  exposed  and  hence  freely  ventilated  field-coils; 
the  other  has  field-coils  embedded  in  the  field-magnets.'  It  is 
known  to  most  motor  designers  that  coils  in  contact  with  iron 
will  dissipate  heat  much  faster  than  when  in  the  open  air.  This  is 
especially  true  of  coils  in  an  enclosed  motor.  I  have  repeatedly 
noticed  that  motor  field-coils  which  have  been  removed  on 
account  of  roasting,  have  shown  the  insulation  in  contact  with 
the  pole  pieces  to  be  in  good  condition,  while  other  sides  were 
badly  roasted.  I  know,  therefore,  that  in  respect  to  ventilation 
of  field-coils,  the  single-phase  motor  is  superior  to  the  direct- 
current  motor.  Smaller  cross-section  of  coils  also  allows  the 
heat  to  be  radiated  better  in  single-phase  motors,  and  the  fact 
that  a  large  part  of  the  loss  in  the  motor  is  concentrated  in  the 
field  iron  will  enable  the  motor  to  dissipate  a  much  larger  amount 
of  heat  for  a  given  temperature-rise  than  will  a  direct-current 
motor. 

"4.  Concerning  'polar  clearances.'  Many  thousands  of 
direct-current  motors  are  to-day  in  operation  with  a  clearance  of 
1/8  in.  to  3/16  in.  between  poles  and  armatures,  and  in  practi- 
cally all  cases  where  more  than  3/16  in.  clearance  is  used  it  is  for 
electrical  reasons.  Further,  while  the  smaller  air-gap  used  for 
single-phase  motors  was  at  first  much  feared,  the  fears  have 
proved  to  be  without  foundation  and  the  present  clearances  of 
from  0.1  in.  to  0.15  in.  have  proved  to  be  ample  and  fully  as 
good  as  0.15  in.  to  0.25  in.  in  direct-current  motors,  because 
there  is  no  unbalanced  magnetic  pull. 

"5.  Concerning  'torque.'  The  torque  of  an  armature  is  the 
pull  it  will  exert  at  one-foot  radius.  Therefore  it  makes  no  dif- 
ference in  the  result  whether  it  is  obtained  with  large  flux  and 
few  armature  conductors,  or  vice  versa. 

"6.  'A  much  larger  diameter  of  armature  and  commutator, 
and  runs  at  a  much  higher  speed.'  This  is  a  very  general  state- 
ment: what  are  the  facts?  The  armature  diameters  ordinarily 
run  from  5  to  15  per  cent,  larger  than  for  direct-current  motors  of 
corresponding  output.  It  is  undoubtedly  true  that  the  armature 
speeds  of  the  earlier  single-phase  motors  were  much  higher 
than  the  speeds  of  corresponding  direct-current  motors;  at  the 
present  time,  however,  the  speed  at  the  nominal  rating  of  the 


312  ELECTRIC    RAILWAY    ENGINEERING. 

motor  is  practically  the  same  as  that  of  direct-current  motors, 
and  the  maximum  operating  armature  speeds  are  within  the 
safe  limits  set  for  direct-current  motors. 

"7.  Concerning  'gear-reduction  and  gear-pitch.'  The  gear- 
reduction  depends,  of  course,  upon  the  speed;  and  as  far  as  gear- 
pitch  is  concerned,  I  wish  to  say  that  the  same  gear-pitch  is  used 
for  single-phase  motors  as  for  direct-current  motors  of  the  same 
capacity. 

"8.  'The  windings  of  one  are  subject  to  electrical  strains  of 
one  character;  in  those  of  the  other  the  strains  are  of  rapidly 
variable  and  alternating  character.'  No  conclusion  is  drawn 
from  this.  It  may  be  of  interest  to  know  that  there  have  been  a 
number  of  instances  where  the  single-phase  motor  has  broken 
down  in  service  on  a  direct-current  section  of  the  line,  necessi- 
tating cutting  it  out  of  the  circuit;  but  when  the  car  reached  the 
alternating-current  section  of  the  line  it  has  been  again  connected 
in  circuit  and  operated  satisfactorily,  thus  indicating  that  the 
electrical  strains  with  alternating  current  are  less  severe  than 
with  direct  current. 

"9  and  10.  Concerning  the  'variable  torque  of  the  single-phase 
motor.'  No  comment  is  made  as  to  the  relative  merits  of  uniform 
or  pulsating  torque.  In  a  recent  discussion  before  the  Institute, 
Mr.  Potter  called  attention  to  certain  characteristics  of  the  torque 
exerted  by  an  alternating-current  motor,  especially  when  it 
reaches  the  slipping  point  of  the  wheels.  It  was  stated  that  there 
is  an  apparent  advantage  in  the  pulsating  torque,  because,  when 
the  motor  starts  to  slip  it  does  not  immediately  decrease  its  mean 
torque,  as  is  done  in  the  case  of  the  direct-current  motor,  but 
slips  in  a  series  of  jerks,  apparently  regaining  the  hold  on  the 
rail  at  every  pulsation. 

"11.  Concerning  the  'number  of  poles.'  The  paper,  states 
that  the  direct-current  motor  has  'two  or  four  main  poles  only.' 
No  direct-current  motors  built  in  the  last  15  years  except  those  on 
the  New  York  Central  locomotives  have  less  than  four  poles. 
The  paper  states  that  the  alternating-current  motor  has 
'eight  to  fourteen  poles.'  The  single-phase  motors  built  by 
the  company  with  which  I  am  connected  have  four  poles  for 
all   sizes  up  to  and  including   125   h.   p.      The  largest  single- 


ALTERNATING    VS.    DIRECT    CURRENT   TRACTION.  313 

phase  motor  thus  far  buih  has  a  capacity  of  500  h.  p.  It  has 
but  12  poles. 

"12.  Concerning  'a  high  torque  while  standing  still.'  As  we 
understand  the  matter,  railway  motors  are  designed  to  move  a 
train  rather  than  to  hold  it  at  rest.  At  the  same  time  we  know 
that  the  single-phase  motor  is  amply  protected  against  mistakes 
of  motormen  in  leaving  the  current  on  the  motor  for  a  half- 
minute  or  so  with  brakes  set. 

''13.  Concerning 'resistance  in  commutator  leads.'  It  is  well 
known  that  the  resistance  leads  used  in  sijigle-phase  armatures 
are  for  the  purpose  of  reducing  to  a  minimum  the-  loss  due  to  the 
transformer  action  in  the  short-circuited  coil.  Their  presence  is 
fully  justified  and  the  efficiency  is  higher  than  it  would  be  if 
they  were  not  used. 

"  14.  This  refers  to  relative  weights  concerning  which  I  shall 
have  something  to  say  farther  on. 

"15.  On  this  point  I  agree  absolutely  with  the  author. 
There  is  one  type  of  construction  to  which  the  single-phase 
motor  is  not  adapted.  This  is  so  far  employed  in  only  a  single 
case.  ♦ 

"More  or  less  is  said  in  the  paper  concerning  the  lower  effici- 
ency of  the  single-phase  motor,  and  inference  might  be  drawn 
that  it  is  about  10  per  cent,  lower  than  that  of  the  corresponding 
direct-current  motor.  Just  to  show  what  modern  motors  are 
capable  of  doing,  I  give  below  in  parallel  columns  the  efficiencies 
of  corresponding  sizes  of  direct-  and  alternating-current  motors 
at  different  percentages  of  their  full-load  torque. 


Per  cent,  of 

full-load 

torque 

Direct  current 
90  h.  p.  motor 

Alternating  cur- 
rent 2S-cycle, 
100  h.  p.  motor 

Direct  current 
200  h.  p.  motor 

Alternating  cur- 
rent   is-cycle, 
200  h.  p.  motor 

■      I2S 

86.25 

82.0 

88.8 

87.3 

100 

86.8 

85.0 

89.0 

88.0 

80 

87.0 

86.0 

89.2 

88.3 

60 

86.5 

86.8 

88.8 

87.7 

40 

85.0 

86.0 

87.0 

85.0 

25 

82.0 

82. 5 

84.0 

82.0 

314  ELECTRIC    RAILWAY   ENGINEERING. 

The  added  weight,  lower  efficiency,  and  lower  acceleration 
for  a  given  capacity  of  motor  are  not  the  only  disadvantages  of 
the  alternating  current  system  from  the  standpoint  of  rolling 
stock.  As  has  been  pointed  out,  it  is  nearly  always  desirable 
that  cars  equipped  for  alternating  current  service  be  able  to  enter 
cities  upon  direct  current.  While  the  alternating  current  single- 
phase  series  motor  makes  an  excellent  direct  current  motor,  the 
control  equipment  for  use  upon  either  system  is  at  best  rather 
complicated  and  its  first  cost,  weight  and  maintenance  relatively 
high.  The  added  complication  of  this  combined  control  is  at 
once  obvious  if  a  comparison  be  made  of  Figs.  104  and  no,  while 
the  tables  listed  below  prove  the  rolling  stock  thus  equipped  to 
cost  28  per  cent  more,  with  a  probable  maintenance  charge  of 
49  per  cent,  more  than  the  600  volt  direct  current  equipment. 

Referring  to  the  1200  volt  direct  current  system,  the  motors 
are  often  of  the  600  volt  type  which  has  been  well  standardized. 
Upon  the  city  systems  they  operate  as  standard  600  volt  equip- 
ment connected  in  parallel  for  full  speed,  while  upon  the  1200 
volt  trolley  they  are  connected  two  in  series  for  full  speed  opera- 
tion. In  cases  where  only  half  speed  operation  is  required 
within  the  city  limits,  1200  volt  motors  similar  to  the  600  volt  type 
are  used,  the  current  capacity,  of  course,  being  less  for  a  given 
car  and  extra  insulation  being  provided  for  the  higher  voltage. 
Although  the  high  voltage  direct  current  equipment  has  not  been 
standardized  and  thoroughly  tried  out  in  practice  as  yet,  the 
dozen  or  more  roads  in  operation  are  apparently  giving  satis- 
factory results,  while  the  first  cost  and  maintenance  cost  are  but 
slightly  greater  than  the  low  voltage  system. 

First  Cost  and  Maintenance. — The  relative  merits  of  the 
three  systems  from  the  standpoint  of  first  cost  and  maintenance 
expenses  can  best  be  illustrated  by  means  of  tables  XXVIII 
and  XXIX  taken  from  a  very  able  discussion  of  the  subject 
before  the  American  Institute  of  Electrical  Engineers  by  W.  J. 
Davis,  Jr.^ 

*  "High  Voltage  Direct  Current  and  Alternating  Current  Systems  for  Interurban 
Railways,"  by  W.  J.  Davis,  Jr.,  A.  I.  E.  E.,  Vol.  XXVI. 


ALTERNATING    VS.    DIRECT    CURRENT    TRACTION. 


;i5 


TABLE  XXVIII. 
CoMPAR-ATrvE  Cost  per  Mile  Single  Track. 


D.  C.  600  V.   D.  C.  1200  V.  I  A.  C.  6600  V. 


Road  bed,  complete  including  grad-  $15,000 
ing,  ballasting,  etc. 

Trolley  and  feeder  installed 3,800 

Track  bonding 600 

Transmission  line  installed 1,5°° 

Substation  installed 2,200 

Power  station  installed 2,450 

Cars  and  equipment 1,800 

Telephone 120 

27,470 
Saving  over  600  volts  D.  C 


^15,000 


pi  5,000 


3,000 

2,100 

530 

480 

1,500 

1,300 

1,600 

600 

2,450 

2,570 

1,970 

2,300 

120 

120 

6,170 

24,470 

1,300 

3,000 

TABLE  XXIX. 

Relative  Oper.ating  Cost  per  Mile  Single  Track  per  Annum. 

(One  hour  headway). 


D.  C.  600  V. 

D.  C.  1200  V. 

A.  C.  6600  V. 

Car  miles  per  day 

64 

64 

64 

Kw.  hours  per  day  at  power  house . .  . 

275 

275 

245 

Cost  of  coal  per  annum 

Cost  of  substation  attendance 

Maintenance  of  motors  and  control. 


Total 

Saving  over  600  V.  direct  current  ex- 
clusive of  fixed  charges. 
Saving  in  fixed  charges 


$470 

$470 

$419 

175 

79 

46 

94 

117 

140 

$739 

666 

605 

76 

134 

137 


315 


Total  annual  saving. 


$213 


449 


The  above  comparative  costs  are  based  upon  the  following 
data: 

Length  of  road,  50  miles  or  more. 

Cars,  52  ft.  over  all,  weighing  21  tons,  without  equipment  or 
load  and  seating  56  passengers. 


o 


1 6  ELECTRIC    RAILWAY   ENGINEERING. 


Car  equipment,  four  75  h.  p.  motors. 
Maximum  speed  on  tangent  level  track,  45  m.  p.  h. 
Schedule  speed,  24  m.  p.  h.  including  stops  and  slow  running 
through  towns. 

Headway,  maximum  service,  one-half  hour. 

Frec|uency  of  stops,  one  in  two  miles. 

Average  energy,  85  watt-hours  per  ton  mile  at  car. 


Spacing  of  substations 

Maximum  trolley  voltage  drop 

Efficiency,  generator  bus  bars  to  cars 
Average  efficiency  car  equipment.  . .  . 
Average  power  factor  of  system 


D.  C.  600  V. 

D. 

C.  1200  V. 

A. 

C.  6600  V. 

10  mi. 

22  mi. 

i   ' 

32  mi. 

259c 

25% 

10% 

71% 

71% 

84% 

75^c 

75% 

73% 

96% 

96% 

85% 

Power  Factor. — The  last  factor  included  in  the  above  list 
emphasizes  one  other  disadvantage  of  the  single-phase  system, 
i.e.,  its  low  uncontrollable  power  factor.  The  direct  current 
system  has  no  apparatus  on  the  car  or  between  the  car  and  the 
converters  to  lower  the  power  factor  and  its  converters  may 
even  permit  the  power  factor  of  the  transmission  line  to  be 
raised.  The  single-phase  system,  with  no  converting  apparatus 
offers  no  means  of  power  factor  control,  while  the  power  factor  is 
lowered  still  further  beyond  the  substation  by  car  motors,  trans- 
former, steel  messenger  or  trolley  if  used  and  rails.  A  lower  power 
factor  means  higher  proportional  current  for  a  given  capacity 
with  increased  first  cost  of  equipment  and  percentage  losses. 

Frequency. — Another  much  discussed  factor  is  that  of  fre- 
quency, if  the  single-phase  system  is  being  considered.  Although 
a  frequency  of  25  cycles  has  been  standardized  for  power  supply 
and  lower  frequency  apparatus  is  at  present  special  and  there- 
fore high  in  first  cost  and  slow  of  delivery,  the  introduction  and 
future  standardization  of  a  15  cycle  frec[uency  for  railway  service 
has  been  seriously  advocated  by  many  railway  engineers  for  the 
following  reasons. 

I.  An  increase  of  from  30  to  40  per  cent,  in  output  of  a  motor 
of  griven  size. 


ALTERNATING    VS.    DIRECT    CURRENT    TR.\CTION.  317 

2.  Consequent  reduction  in  motor  capacity  required. 

3.  Consequent  reduction  in  first  cost  of  motor  equipment. 

4.  Higher  motor  efficiency. 

5.  Higher  motor  power  factor. 

6.  Better  commutation. 

7.  Less  dead  weight  on  axles. 

8.  Lower  line  losses. 

In  contrast  to  these  advantages  of  low  frequency  may  be  listed 
the  impossibility  of  supplying  lighting  loads  from  the  same 
generators  with  this  frequency,  the  already  established  standard 
of  25  cycles,  unsatisfactory  turbine  design  in  small  sizes  and  the 
higher  cost  and  greater  weight  of  transformers. 

At  present  there  is  no  15  cycle  railway  system  in  this  country 
and  it  rests  with  the  engineers  of  the  future  to  decide  whether  the 
above  advantages  of  low  frequency  are  to  dominate  the  selection 
of  equipment  for  the  individual  roads  if  alternating  current 
traction  be  determined  upon.  The  opinion  has  been  often 
expressed  by  prominent  engineers  that  if  the  single-phase  rail- 
way motor  can  be  improved,  the  elimination  of  the  converting 
apparatus  in  the  substation  and  the  lower  first  cost  of  the  entire 
system  will  soon  bring  about  a  more  general  adoption  of  single- 
phase  traction.  Whether  the  lowering  of  the  frequency  to  15 
cycles  is  the  means  to  this  end  or  not  is  yet  to  be  decided. 

In  conclusion,  it  may  be  said  that  the  tendency  in  electric  trac- 
tion as  in  every  other  branch  of  electrical  development  is  toward 
higher  voltages.  The  advocates  of  direct  current  traction  point 
out  the  advantages  of  the  1200  volt  system  over  the  once  almost 
universal  system  operating  at  600  volts.  In  a  recent  paper  before 
the  American  Institute  of  Electrical  Engineers  a  conservative 
estimate  of  the  economy  obtained  by  a  1200  volt  direct  current 
system  as  compared  with  the  600  volt  system  as  far  as  the  factors 
are  concerned  which  are  dependent  upon  choice  of  system  was 
given  as  follows.^ 

First  cost,  10  to  20  per  cent. 

Fixed  charges,  10  to  18  per  cent. 

Operation  and  maintenance,        10  to  15  ])er  cent. 

'  "The  1200  volt  railroad:  A  Study  of  ItsX'alue  for  Intc'rur!)an  Railways,"  by 
Charles  E.  Evelcth,  A.  I.  E.  E.,  Vol.  XXIX. 


3l8  ELECTRIC   RAILWAY   ENGINEERING. 

If  the  argument  be  carried  but  a  step  farther,  the  favored 
system  of  the  near  future  would  naturally  be  that  one  capable 
of  transmitting  power  to  the  car  at  still  higher  voltages,  which 
seems  to  point  at  present  to  alternating  current  propulsion  of  cars. 
This  tendency  in  the  near  future  should  be  greatly  strengthened 
by  the  possible  elimination  (with  the  alternating  current  system) 
of  the  converter  substation  and  its  attendant  operating  troubles 
and  expense  and  the  lower  first  cost  of  the  latter  system  where 
taken  as  a  whole.  All  history  of  science  and  engineering  is 
opposed  to  the  feeling  that  the  present  condition  of  the  alternating 
current  system  is  as  efficient  and  simple  as  it  can  be  made  and 
it  therefore  seems  quite  probable  that  the  few  unsatisfactory 
features  of  the  alternating  current  motor  and  control  design  will 
soon  be  overcome  and  the  single-phase  system  enjoy  a  much 
extended  application  to  long  distance  traction.  It  will  remain 
for  the  consulting  engineer,  however,  to  decide  in  each  individual 
case  upon  the  merits  of  the  three  or  more  systems,  and  the  above 
statements  should  not  be  interpreted,  therefore,  as  a  prediction 
that  alternating  current  traction  will  be  eventually  installed  in 
all  interurban  developments  nor  that  it  necessarily  is,  or  ever 
will  be,  the  solution  of  trunk  line  electrification. 


CHAPTER  II. 

Electric  Traction  OxN  Trunk  Lines. 

The  late  E.  H.  Harriman  is  quoted  in  the  New  York  Times 
as  having  said: 

"But  perhaps  it  is  chimerical  to  think  now  of  rebuilding  the 
railroads  of  the  entire  country,  and  of  replacing  the  entire  rail- 
road equipment.  If  so,  what  is  the  best  thing?  Obviously, 
electricity.  And  I  believe  that  the  railroads  will  have  to  come 
to  that,  not  only  to  get  a  larger  unit  of  motor  power  and  of  dis- 
tributing it  over  the  train  load,  but  on  account  of  fuel.  That 
brings  up  another  phase  of  the  existing  conditions.  We  have 
to  use  up  fuel  to  carry  our  fuel,  and  there  are  certain  limitations 
here  just  as  much  as  there  are  in  car  capacity  or  motive  power, 
particularly  when  you  consider  the  distribution  of  the  coal  pro- 
ducing regions  with  respect  to  the  major  avenues  of  traffic.  The 
great  saving  resulting  from  the  use  of  electricity  is  apparent, 
quite  aside  from  the  matter  of  increasing  the  tractive  power  and 
the  train  load. 

"The  only  relief  which  can  be  obtained  through  economics 
of  physical  operation  must  come  through  the  outlay  of  enormous 
amounts  of  money  such  as  would  be  involved  in  a  general  electri- 
fication or  change  of  gauge." 

This  statement  coming  from  such  an  eminent  steam  railroad 
authority,  together  with  the  already  completed  electrification  of 
the  terminals  of  the  three  large  steam  railroads  entering  New 
York,  the  Hoosac  Tunnel  of  the  New  York,  New  Haven  and 
Hartford  Railroad,  the  Cascade  Tunnel  of  the  Great  Northern 
and  many  other  sections  of  former  steam  railroads  throughout 
the  country  must  convince  the  most  prejudiced  opponent  of  elec- 
trification that  the  time  has  come  for  the  serious  study  of  the  prob- 
lem of  trunk  line  electrification.  Thus  far  the  electrification  of 
steam  roads  has  been  adopted  to  meet  special  requirements  or  to 
solve  peculiar  problems  in  traction,  such  as  the  necessity  of  in- 

319 


320  ELECTRIC    RAILWAY   ENGINEERING. 

creased  ser\'ice  in  large  terminals,  the  avoidance  of  smoke  in 
tunnels  and  the  decrease  of  headway  upon  single  track  mountain 
grades.  It  may  be  safely  predicted,  however,  that  these  special 
problems  will  gradually  increase,  the  electrified  terminal  divisions 
gradually  encroach  upon  the  trunk  line  and  eventually  all  will  be 
electrically  operated. 

Probably  the  two  paramount  questions  in  the  minds  of  steam 
railroad  directors  in  connection  with  this  problem  are: 

1.  Can  the  service  be  improved  with  electric  traction? 

2.  What  will  it  cost  to  change  and  to  operate  and  maintain 

the  new  system  when  installed  ? 
While  it  seems  advisable  to  consider  these  questions,  especially 
the  second,  more  in  detail  subsequently,  a  few  of  the  minor  ad- 
vantages of  electric  traction  on  trunk  lines,  most  of  which  are 
involved  in  the  first  question  of  possible  improved  service,  will  be 
first  considered.  The  outline  of  the  following  brief  discussion 
is  one  presented  in  great  detail  in  the  very  valuable  paper  by 
Messrs.  Stillwell  and  Putnam  before  the  American  Institute  of 
Electrical  Engineers.^ 

The  factors  entering  into  passenger  service  which  contribute 
to  the  earning  power  of  the  electrified  road  to  a  greater  extent 
than  the  steam  railroad  are : 

Frec[uency  of  service. 

Speed. 

Comfort  of  passengers. 

Safety. 

Reliability  of  service. 

Increased  capacity  of  line. 

Frequency  of  stops. 

Convenient  establishment  of  feeder  lines. 

Frequency  of  Service. — Experience  with  high  speed  inter- 
urban  lines  paralleling  steam  lines,  but  offering  much  more  fre- 
quent service  as  illustrated  in  Table  III,  Part  I,  leads  to  the  con- 
clusion that  frequent  service  creates  traffic  and  therefore  increases 
earning  power.  The  frequent  service  ofltered  by  an  electrified 
system  is  usually  impractical  with  steam  operation. 

'  "On  the  Substitution  of  the  Electric  Motor  for  the  Steam  Locomotive,"  by 
Lewis  B.  Stilhvell  and  Henry  St.  Clair  Putman,  A.  I.  E.  E.,  Vol.  XXVL 


ELECTRIC    TR.\CTIOX    ON    TRUNK    LINES.  32 1 

Speed. — Higher  average  speeds  are  possible  and  practical  in 
electric  service  for  four  principal  reasons. 

a.  The  absence  of  reciprocating  parts  reduces  danger  of  the 
locomotive  leaving  the  track. 

b.  The  absence  of  reciprocating  parts  reduces  the  maintenance 
of  the  track  and  the  liability  of  broken  rails. 

c.  The  more  rapid  acceleration  permits  higher  average  speed 
with  the  same  number  of  stops,  or  more  stops  with  the  same 
schedule  speed. 

d.  For  heavy  trains  requiring  two  locomotives,  high  speeds 
can  be  maintained  by  means  of  the  multiple-unit  control  system. 
This  is  unsafe  with  two  steam  locomotives,  as  both  engines  cannot 
be  controlled  by  a  single  engineer. 

Comfort  of  Passengers. — The  general  comfort  of  passengers 
is  greatly  enhanced  by  the  following  features  of  electric  traction: 

a.  Elimination  of  smoke  and  cinders. 

b.  Improved  ventilation  of  cars  made  possible  because  of  the 
absence  of  smoke  and  cinders. 

c.  More  efficient  and  satisfactory  car  lighting  possible,  although 
unfortunately  not  always  provided. 

d.  Easily  controlled  car  heating. 

Safety. — Several  very  notable  elements  of  danger  which  arc 
present  in  steam  traction  are  eliminated  when  electrification  is 
complete. 

a.  The  power  may  be  shut  off  by  the  train  dispatcher  to  avoid 
collision. 

b.  The  results  of  the  absence  of  reciprocating  parts  which 
permit  higher  speeds  to  be  maintained  as  outlined  under  the 
caption  "Speed"  also  reduce  the  probability  of  accident. 

c.  If  a  collision  occurs,  the  power  may  be  promptly  cut  off  if 
it  is  not  accomplished  automatically,  as  is  usually  the  case. 

d.  The  absence  of  the  intense  fire  of  the  locomotive  reduces 
the  probability  of  fire  in  the  wreckage. 

e.  The  elimination  of  hot  water  and  steam  in  locomotive  and 
heating  system  reduces  the  dangers  often  resulting  from  such 
sources. 

f.  The  absence  of  smoke  in  tunnels  prevents  errors  in  reading 
signals  from  that  cause. 


322  ELECTRIC    RAILWAY   ENGINEERING. 

g.  Less  likelihood  of  fire  from  electric  lighting  than  from  the 
oil  or  gas  lamps  commonly  used  upon  steam  roads. 

h.  The  presence  of  a  source  of  electrical  power  along  the 
roadway  and  the  necessary  employment  of  electrically  trained 
maintenance  crews  should  decrease  the  first  cost  and  maintenance, 
and  therefore  increase  the  use  of  automatic  block  signals. 

It  must  be  remembered,  however,  that  in  contrast  to  these 
advantages,  the  electrical  distribution  system,  especially  the 
third  rail,  offers  a  danger  not  present  in  steam  railroad  operation. 
Whereas  the  third  rail  may  be  protected,  thereby  reducing  the 
danger  under  normal  operation  to  a  minimum,  such  protection 
would  avail  little  in  the  case  of  a  wreck.  Under  these  circum- 
stances the  automatic  circuit  breakers  must  be  relied  upon  to 
disconnect  the  section  from  the  source  of  supply  before 
serious  physiological  effects  are  produced  or  fires  started  in  the 
wreckage. 

Reliability  of  Service. — Comparison  of  the  train  delays  from 
all  causes,  both  electrical  and  mechanical,  before  and  after  elec- 
trification upon  the  few  roads  which  have  been  operating  suffi- 
ciently long  by  electricity  to  guarantee  dependable  results  points 
to  the  conclusion  that  the  service  is  more  reliable  after  electri- 
fication than  before. 

■  For  example,  upon  the  Manhattan  division  of  the  Interborough 
Rapid  Transit  system  of  New  York  after  electrification,  the 
delay  during  the  most  severe  months  of  the  year  for  the 
exposed  third  rail  system  was  but  72  per  cent,  of  that  under 
steam  operation,  expressed  in  train  minutes,  although  an 
increased  car  mileage  of  37  per  cent,  was  maintained  with  the 
electric  service. 

Upon  the  electrified  section  of  the  New  York,  New  Haven 
and  Hartford  Railroad  during  the  heaviest  traffic  day  of  the  year 
occasioned  by  the  annual  foot-ball  game  at  New  Haven,  128 
regular  trains  and  30  special  trains  were  operated  between  New 
York  and  New  Haven  in  1908  with  but  two  delays  totaling  17 
minutes,  while  in  1909,  155  trains  were  run  with  no  delays 
whatever. 

The  electrified  system  of  the  Grand  Trunk  Railway  in  the 
St.  Clair  Tunnel  has  operated  six  single-phase  locomotives,  each 


ELECTRIC    TRACTION    OX    TRUNK    LINES.  323 

averaging  about  loo  miles  a  day  for  a  year,  with  but  one  delay 
and  that  of  eight  minutes  duration. 

When  it  is  remembered  that  the  train  detention  due  to  motive 
power  troubles  expressed  in  a  percentage  ratio  of  the  actual 
motive  power  trouble  delay  in  minutes  to  total  train  minutes 
delay  from  all  causes  upon  an  electrified  road  is  but  8.5  per  cent, 
and  that  this  small  percentage  has  been  materially  reduced  over 
that  of  steam  service,  it  may  safely  be  said  that  present  operation 
of  electric  locomotives  is  very  reliable. 

Increased  Capacity  of  Line. — One  of  the  marked  advan- 
tages of  electric  traction  is  its  large  tractive  effort  for  a  given  size 
and  weight  of  equipment.  While  this  feature  is  pronounced  in 
the  electric  locomotive  because  of  the  elimination  of  the  tender 
and  the  possible  use  of  such  a  design  as  to  throw  practically  all 
the  weight  of  the  locomotive  upon  the  drivers,  the  effect  is  still 
more  marked  if  motor  cars  be  used,  thus  making  practically  the 
entire  weight  of  train  available  for  tractive  effort  between  wheels 
and  track.  With  this  relatively  great  tractive  effort,  much 
higher  rates  of  acceleration  are  possible,  which  in  turn  permit 
smaller  headway  between  trains  and  increased  traffic  capacity 
for  a  given  track. 

This  is  of  particular  value  upon  heavy  grades  of  the  single 
track  roads  of  the  West,  where  electrification  permits  so  great 
an  increase  in  traffic  over  an  existing  single  track  that  it  obviates 
the  necessity  of  double  tracking  the  road  for  some  time  to  come. 
In  this  case  the  cost  of  electrification  may  be  balanced  directly 
against  the  cost  of  a  second  track,  which  in  the  mountains  of  the 
West  becomes  a  formidable  figure. 

Further,  the  length  of  freight  trains  using  the  steam  locomotive 
is  limited  by  the  strength  of  the  draft  gear.  With  the  use  of  two 
or  more  electric  locomotives  at  the  head  of  a  train,  or  if  the  limit 
of  the  draft  gear  is  reached,  possibly  the  introduction  of  several 
locomotives  throughout  the  length  of  the  train,  all  operated  by 
means  of  the  multiple  unit  control  from  the  leading  engine  will 
probably  make  possible  a  greatly  increased  freight  traffic  over  a 
given  road,  thus  increasing  the  freight  as  well  as  the  passenger 
capacity  of  the  line. 

Frequency  of  Stops. — The  ability  of  the  electrically  operated 


324  ELECTRIC    RAILWAY    ENGINEERING. 

train  to  make  more  frequent  stops  and  thus  better  accommodate 
the  riding  public  without  reducing  the  schedule  from  that  of  the 
steam  road  has  already  been  explained. 

In  addition  to  the  above  advantage  in  some  instances  it  is  pos- 
sible to  interconnect  the  local  railway  system  with  the  electrified 
road  in  such  a  way  as  to  transport  passengers  more  nearly  to 
their  destination  without  change. 

Both  of  the  above  features  tend  to  increase  the  traffic  and 
resulting  earnings  of  the  road. 

Convenient  Establishment  of  Feeder  Lines. — With  the 
reduced  cost  of  power  possible  with  an  electrified  trunk  line, 
short  branches  of  present  steam  roads  or  existing  suburban  or 
interurban  lines  may  be  operated  electrically  much  more  econom- 
ically tha,n  at  present.  The  large  and  efficient  organization  of 
the  trunk  line  system  also  adds  materially  to  this  possibility. 
These  short  branch  roads  then  become  valuable  feeders  to  the 
through  trunk  line. 

Still  further  economy  and  convenience  to  passengers  in  such 
branch  line  operation  may  often  be  brought  about  by  adding 
branch  line  motor  cars  to  the  through  train  at  junction  points, 
operating  the  entire  train  thus  made  up  by  the  multiple  unit 
system. 

Improvement  of  Service. — It  is  believed  that  the  first  question 
to  be  asked  by  the  directors  of  a  steam  road  to  which  reference 
was  made  early  in  the  chapter  has  been  satisfactorily  answered 
by  the  above  improvements  in  the  service,  which  have  been  shown 
to  be  possible  upon  electrified  roads. 

The  possibility  of  increased  draw  bar  pull  and  more  rapid 
acceleration  should,  however,  have  more  detailed  analysis,  for  it 
is  largely  with  regard  to  these  features  that  service  may  be  im- 
proved and  earnings  increased  and  therefore  it  is  to  these  features 
to  which  the  present  steam  railroad  officials  look  at  a  time  when 
service  can  no  longer  be  increased  with  present  locomotives  since 
the  latter  have  practically  reached  their  maximum  size  and  effi- 
ciency. 

DeMuralt  has  worked  out  the  following  table  to  illustrate  the 
relative  values  of  maximum  tractive  eft'ort  available  with  various 
types  of  locomotives  operating  on  level  track  at  60  m.  p.  h.  to 


ELECTRIC    TRACTION    OX    TRUNK    LINES. 


0^3 


which  the  author  has  added  the  last  cohimn,  which  more  readily 
compares  the  locomotives  upon  a  standard  basis  of  unit  weight. 
The  locomotives  selected  for  this  calculation  were  the  New  York, 
New  Haven  and  Hartford  single-phase  and  the  New  York  Cen- 
tral direct  current  locomotives  operating  in  1907  and  a  three- 
phase  locomotive  operated  by  the  Italian  State  Railways  com- 
pared with  the  most  powerful  Atlantic  and  Pacific  type  steam 
locomotives  constructed. 

TABLE  XXX. 
Comparison  of  Electric  .-^nd  Steam  Locomotives. 


Single-phase.    . 
Direct  current. 

.■\tlantic 

Pacific 

Three-phase. . . 


Max.  Tract. 

effort  lbs. 


4250 
6000 
9250 
9750 
93  7  5 


Wt.  of  loco- 
motive and 
tender  tons 


Max.  possible 

Trail,   wt. 
tons 


165 

258 
382 

398 

457 


Max.  T.  E.  per 
ton  wt.  of  loco- 
motive 


so 
63. 


56.6 
98.6 


From  the  above  tabic  it  will  be  seen  that  the  single-phase 
locomotives  built  at  that  time  had  a  13  per  cent,  lower  tractive 
effort  and  the  direct  current  locomotive  a  10  per  cent,  higher 
effort  than  the  most  powerful  steam  locomotive,  while  the  three- 
phase  locomotive  was  capable  of  exerting  71.5  per  cent,  greater 
pull  than  the  latter  based  upon  unit  weight  of  locomotive. 

As  values  of  maximum  tractive  effort  have  since  been  more 
than  doubled  in  the  case  of  the  single-phase  type  and  the  Pennsyl- 
vania locomotive  with  its  motors  above  the  drivers  has  been  intro- 
duced with  a  tractive  effort  30  per  cent,  greater  than  the  direct 
current  locomotive  of  the  above  table,  it  may  be  seen  that  the 
largest  steam  locomotives  are  now  far  excelled  in  this  respect. 

Again,  comparing  present  motor  car  operation  in  heavy  service 
with  that  of  the  steam  locomotive  it  is  found  that  an  eight  car 
electric  train  in  the  New  York  subway  develops  a  draw  bar  pull 
more  than  double  the  maximum  value  possible  with  the  largest 
locomotive  on  the  Erie  railroad. 

A  most  inspiring  and  graphic  demonstration  of  the  ability  of 


326  ELECTRIC   RAILWAY   ENGINEERING. 

the  New  York  Central  locomotive,  particularly  in  rapid  ac 
celeration,  was  the  often  quoted  test  carried  out  in  1904  on  the 
New  York  Central  Railroad  when  electric  locomotive  No.  6000, 
drawing  eight  Pullman  coaches  with  a  total  train  weigh  of  478 . 5 
tons,  after  reaching  the  same  speed  as  the  New  York  Central 
fast  express  was  allowed  to  attain  its  maximum  speed  and  was 
found  to  gain  a  full  train  length  in  the  distance  of  one  mile. 

Cost  of  Electrification  and  Operation. — Granted  that  the 
service  can  be  improved  and  the  capacity  of  a  road  increased 
with  electric  traction  as  pointed  out  above,  an  answer  to  the  sec- 
ond question  must  be  found,  i.e.,  "What  will  it  cost  to  change 
and  to  operate  and  maintain  the  new  system  when  installed?" 

The  first  cost  of  the  change  will  vary  greatly  with  local  con- 
ditions and  in  any  case  would  probably  be  prohibitive  if  under- 
taken for  a  complete  trunk  line  system  at  once.  Experimentation, 
if  necessary  at  all,  should  be  carried  out  upon  some  of  the  less 
important  branches  and  the  electrical  rolling  stock  secured  a 
portion  at  a  time.  It  has  even  been  suggested  that  as  the  pur- 
chase of  new  steam  locomotives  to  replace  those  worn  out  or 
considered  obsolete  is  usually  treated  by  steam  roads  as  an 
operation  charge  and  not  a  charge  against  capital,  the  electrical 
rolling  stock,  or  a  large  portion  of  it,  might  be  secured  in  like 
manner  and  no  great  capital  investment  made  for  this  portion 
of  the  new  system. 

The  American  Institute  of  Electrical  Engineers  was  partic- 
ularly fortunate  at  its  191 1  annual  convention  to  have  presented 
by  the  Pennsylvania  Railroad  through  Mr.  B.  F.  Wood,  a  very 
detailed  statement  of  the  first  cost  and  operating  expenses  of  the 
electrification  of  the  West  Jersey  and  Seashore  Railroad.  While 
the  figures  for  a  larger  trunk  line  operating  locomotives  in  place 
of  motor  car  trains  would  vary  somewhat  from  those  applying 
to  this  road  as  illustrated  in  the  discussion  which  follows,  the 
costs  of  this  particular  electrification  which  are  the  first  to  be 
made  public  in  complete  detail  are  well  worthy  of  careful  study. 
Tables  XXXI  and  XXXII  give  total  and  unit  costs  of  electri- 
fication, while  operating  expenses  are  well  analyzed  in  Tables 
XXXIII  to  XXXVI  inclusive.  The  costs  apply  to  a  total  of  150 
miles  of  single  track  upon  which  47  to  52  ton  cars  are  operated 


ELECTRIC    TR.A.CTION    OX    TRUNK    LINES.  327 

in  trains  with  two  200  h.  p.  motors  per  car  controlled  with  the 
multiple  unit  equipment.  The  power  station  is  of  8000  k.w. 
capacity  supplying  power  to  eight  substations  ranging  from  1000 
to  2500  k.w.  each.  The  distribution  voltage  on  the  third  rail 
system  is  675  volts  direct  current. 

TABLE  XXXI.  1 

Cost  of  Electrification. 

Power  stations: 

Building,  stacks,  coal  and  ash  handling  machinery $354,000 

Equipment 640,900 

Total $994,900 

Transmission  line 241,500 

Substations: 

Buildings 72,000 

Equipment 419,560 

Total 491,560 

Third  rail 557.636 

Overhead  trolley 80,500 

Track  bonding *. 102,659 

Cars 1,135,900 

Car  repair  and  inspection  sheds 46,674 

Right-of-way,  additional 592,100 

Reconstructing  tracks 763,800 

Constructing  new  tracks 2,071,000 

Terminal  facilities  and  changes  at  stations 252,400 

Signals  and  interlocking  plants 561,900 

Changing  telegraph  and  adding  telephone  facilities 105,100 

Fencing  right-of-way,  cattle  guards,  etc 88,400 

Miscellaneous  items 44,200 

Total 8,130,229 

TABLE  XXXII.  I 
Unit  Costs  of  Electrification. 

Power  station,  cost  per  kw $124.36 

Transmission  line,  cost  per  mile 3,4^5  00 

Substations,  building  and  equipment  cost  per  kw. .  .  .  28.90 

Third  rail,  cost  per  mile 4,235 .00 

Overhead  trolley,  cost  per  mile 4,120.00 

Track  bonding,  cost  per  mile 684.50 

Cars,  including  electrical  equipment  each 12,214.00 

'"Electrical  Operation  of   the  West    Jersey  and  Seashore  Railroad,"  by  B.  F 
Wood.     A.  I.  E.  E.  \'ol.  XXX. 


128 


ELECTRIC    RAILWAY  ENGINEERING. 


TABLE  XXXIII.  1 
Power  Station  Operation  and  Maintenance  Cost. 


Year 


Items 


Total 


■  Boiler  room 

Turbine 

Labor.  J  Electrical 

Supervision  janitors  and  watchmen. 


14,742.36 

10,010.81 

1,661 .02 

2,756-23 


Material. 


Coal 

Water 

Lubricants 

Misc.  material 

Misc.  charges 

Total  operating  material . 

Total  operation 


Labor . 


Building 

Boiler  room 

Turbine 

Auxiliary  apparatus 

Electrical 

Piping 

Miscellaneous 

Total  maintenance  labor. 


MateriaL 


Building 

Boiler  room 

Turbine 

Auxiliar}'  apparatus 

Electrical 

Piping 

Miscellaneous 

[  Total  maintenance  material. 
Total  maintenance 


Total  labor 

Total  material 

Total  labor  and  material  station  proper . 
Other  items  charged  to  station  accounts 

Total 

Net  output 

Lbs.  coal  per  k\v-hr 

Cost  of  coal  per  2000  lbs 


102,715.31 

500 . CO 


2,238.44 

1,700.49 


107,154-24 


326.29 
1,550-44 

836.11 

844 • 17 
195-30 
691.94 
187.30 


4,631-55 

146.63 
2,493-23 
1,597-52 

2,066. 13 

3,046.44 

383 -97 
599-06 


10,332. ( 


14,964  -  53 

33,801.97 

117,487 .22 

151,289. 19 

2,160.60 

153,449-79 
28,312,500 

3-246 
$2,235 


Cent  per 

k\v-hr. 


o  035 
0.006 


Total  operating  labor 29,170.42    ,       0.103 


0-363 
0.002 


0.007 
0.006 


0-378 


136,324.66   j       0.481 


o  .001 
0.005 
0.003 
0.003 

O.OOI 

0.002 

O.OOI 


0.016 

0.001 
0.009 
0.006 
0.007 

O.OII 

0.001 
0.002 


0-037 


0-053 


0 

119 

0 

415 

0 

534 

0 

008 

0 

542 

*" Electrical  Operation  of  the  West  Jersey  and  Seashore  Railroad,"  by  B.  F. 
Wood.     A.  I.  E.  E.  Vol.  XXX. 


ELECTRIC    TRACTION    ON    TRUNK    LINES. 


329 


TABLE  XXXIV.' 
Cost  of  Train  Oper.\tion  pkr  Car  Mile. 

Year  1909. 


" 

i2 

0) 

w 

es 

1 

•o 

CU 

U     (0 

c 

^ 

0 

si 
11 

+J 

c! 

0 

0 
'S  i2 

■«3  s-i 

Q> 

i 

<U     ui 

(U 

■> 

1 
c   1 

c. 

0 

C 
<u 

a 

X 

c 
t 

0 

0 

? 

3 

3 

<U     V 

0 

w 

'O  t;; 

h 
q 

"cS 

B 

60 

|g 

5" 
Pi 

0    ° 

5§ 

0 

2 

£  = 

^ 

0 

0 

0 

Avg. .  . 

0.68 

1 .  10 

0.2s 

4-30 

0.33 

0.8S 

1.44 

0.69 

9.67 

'9.08 

1S.75 

4,107,609 

3-457 

i 

Year  1910. 


Avg...    0.66     1. 01    o..'7    ,5.33    0-43   0-91  1-52   0-67   8.80119.3918.19  1 4.552,532  351 


TABLE  XXXV.  1 

Cost  of  Tr.\nsmission  System;  Maintenance. 
1910. 


High  tension      I  Overhead  trolley 


Third  rail 


Running  track 
bonding 


Total  Per  Total      |    Per    |     Total         j    Per    '      Total      :    Per 

mile  :    mile    1  '    mile  mile 


Total  and  avg.   $3,444.57    $4.10  $4, 
per  mi.  per  mo. 


JS.16   $36.70510,864.13    S6.46    $2,445.72  ,  $1.36 


TABLE  XXXVI. ' 

Cost  of  subst.xtion  Oper.^tion  and  Maintenance. 
1910. 


Total  for  eight  substations 


Operation       Maintenance 


Total 


Cost  per      Substation  output  kw-hr. 
kw-hr.  67s  volts  (direct-current 


Year $20,852.31     '$3,607.30       $24,459.61   $0.001082  21,972,300 


'"Electrical  Operation  of  the  West  Jersey  and  Seashore  Railroad,"  by  B.  F 
Wood.     A.  I.  E.  E.  Vol.  XXX. 


330  ELECTRIC    RAILWAY   ENGINEERING. 

In  order  to  obtain  an  idea  of  the  magnitude  of  the  cost  of  electri- 
fication of  the  trunk  lines  of  the  United  States,  attention  should  . 
be  given  to  the  estimates  which  have  been  made  by  Stillwell  and 
Putnam,  ^  particularly  with  regard  to  the  effect  upon  this  cost  of 
a  reduction  of  frequency  to  15  cycles.  Their  estimate  is  based 
upon  a  continuous  output  of  2,100,000  k.w.  from  all  the  power 
stations  combined.  The  power  station  apparatus  such  as  tur- 
bines, transformers,  meters,  etc.,  which  would  be  effected  by 
frequency  is  estimated  at  S30  per  k.w.  at  25  cycles,  or  $t,^  at 
15  cycles.  Substation  transformers  would  be  increased  one- 
third  in  first  cost,  so  that  the  cost  of  electrical  equipment  in 
power  house  and  substations  would  be  increased  from  $70,000,000 
to  S8o,ooo,ooo,  with  the  decrease  in  frequency.  The  assumption 
is  made,  although  open  to  serious  question,  that  one  electric 
locomotive,  costing  $25,000,  will  do  the  work  of  two  de- 
signed for  steam  operation.  With  this  assumption  the  aggregate 
cost  of  electric  locomotives  will  be  $600,000,000  at  25  cycles. 
The  cost  of  these  locomotives  would  be  reduced  with  the  change 
in  frequency  by  possibly  $1,000  each.  Storer  places  this  figure 
at  $5,000.  With  the  former  and  more  conservative  estimate  the 
saving  with  the  lower  frequency  on  locomotives,  is  $24,000,000, 
which  is  more  than  double  the  increase  in  cost  of  power  station 
and  substation  equipment.  This  points  toward  a  conservatively 
estimated  saving  of  $14,000,000  if  the  lower  frequency  be  chosen. 

Going  a  step  farther  into  these  rather  astounding  estimates 
the  power  station  equipment  for  this  general  electrification  figured 
at  the  low  value  of  $100  per  k.w.  would  amount  to  $210,- 
000,000,  with  possibly  an  added  $63,000,000  for  substations  and 
$600,000,000  for  locomotives,  etc.,  reaching  a  grand  total  esti- 
mated at  one  and  one-half  billions  of  dollars  for  the  entire  under- 
taking. 

Upon  the  other  hand,  if  the  figures  quoted  by  Murray^  based 
upon  actual  observations  of  maintenance  and  operation  costs 
upon  the  electrified  section  of  the  New  York,  New  Haven  and 

^"On  Substitution  of  the  Electric  Motor  for  the  Steam  Locomotive,"  by 
Lewis  B.  Stilhvell-and  Henry  St.  Clair  Putnam,  A.  I.  E.  E.  Vol.  XXVI. 

^  Discussion  by  W.  S.  Murray  upon  paper,  "On  the  Substitution  of  the  Electric 
Motor  for  the  Steam  Locomotive."     A.  I.  E.  E.  Vol.  XXVI. 


ELECTRIC    TRACTION    ON    TRUNK    LINES. 


331 


Hartford  Railroad  are  given  serious  consideration,  it  will  be  found 
that  the  above  tremendous  outlay  is  not  confined  to  improve- 
ments in  service  and  increased  capacity  of  road  alone,  but  that 
it  will  return  dividends  in  the  form  of  lowered  operating  costs  and 
maintenance  charges  as  well.  For  example,  Table  XXXVII. 
indicates  the  saving  in  coal  per  annum  measured  at  the  power 
house  of  the  electrified  system  as  compared  with  that  used  in  the 
fire  box  of  the  steam  locomotive  performing  the  same  schedule. 

TABLE  XXXVII. 


Ton  miles 
per  annum 

Tons  coal 

steam 

traction 

Tons  coal 
electric 
traction 

Cost  coal 
steam 
traction 

Cost  coal 
electric 
traction 

Saving  of 

elec.  over 

steam 

Express 

Express  local. .  . 
Express  freight. 

592,240,000 

348,000,000 

2,223,000,000 

57,447 

58,300 

187,844 

29,870 

28,600 

139,010 

$183,830 
186,560 
563,530 

$89,620 

85,800 

417,030 

$94,210 
100,760 
146,500 

Total  saving. 

$341,470 

This  means  that  the  saving  in  coal  alone  on  a  short  section  of 
but  one  trunk  line  will  amount  to  $341,470  per  annum  due  to  elec- 
trical operation,  while  further  study  of  gains  in  maintenance 
leads  to  the  conclusion  that  the  cost  of  repairs  of  the  electrical 
equipment  will  be  but  one-third  or  one-fourth  that  of  steam  loco- 
motives. These  two  savings  alone  when  capitalized  for  all  the 
trunk  lines  of  the  country  will  go  a  great  way  toward  balancing 
the  seemingly  excessive  first  cost  of  electrification  estimated  above. 

Standardization. — If  the  prediction  made  earlier  in  this  dis- 
cussion prove  true,  and  the  electrified  terminal  and  tunnel  divisions 
of  trunk  lines  gradually  expand,  as  they  seem  to  be  expanding 
already,  and  ultimately  they  desire  to  merge  together  and  ex- 
change equipment  in  order  that  through  service  may  be  main- 
tained over  several  roads,  if  one  system  has  selected  the  600  volt 
direct  current  third  rail  supply  as  in  the  case  of  the  New  York 
Central,  and  another  the  high  voltage  alternating  current  trolley 
typical  of  the  New  York,  New  Haven  and  Hartford,  but  possibly 
of  another  frequency  and  still  other  mountain  divisions  expand 
the  territory  operated  with  three-phase  power,  it  can  readily  be 
seen  that  a  situation  will  result  fully  as  serious  as  the  attempted 


332  ELECTRIC    RAILWAY    ENGINEERING. 

combination  not  long  ago  of  roads  of  different  track  gauges  and 
of  cars  with  and  without  standard  air  brake  equipment.  George 
Westinghouse  did  not  sound  the  warning  of  standardization  any 
too  early,  therefore,  in  his  recent  paper  before  the  London  con- 
vention previously  alluded  to,  when  he  said : 

"For  the  present  it  may  be  a  matter  of  little  moment  whether 
different  systems  have  their  contact  conductors  in  the  same 
position,  or  whether  the  character  of  the  current  used  is  the  same 
or  different.  As  previously  stated  in  the  early  days  of  railroading, 
it  was  of  little  consecjuence  whether  the  tracks  of  the  different 
systems  in  various  parts  of  the  country  were  alike  or  unlike,  but 
later  it  did  make  a  vital  difference,  and  the  variation  resulted  in 
financial  burdens  which  even  yet  lie  heavily  on  some  railways. 
It  is  this  large  view  into  the  future  of  electrical  service  which 
should  be  taken  by  those  responsible  for  electric  railway  develop- 
ment." 


INDEX. 


Air  brake  equipment,  265 
Alternating  versus  direct  current  trac- 
tion, 305 

Ballast,  208 

Block  signals,  iq4 

Boilers,  162 

Bonds  and  bonding,  170 

amalgam,  173 

cast,  173 

compressed  terminal,  171 

cross  bonding,  177 

soldered  and  brazed,  171 

testing,  175 

welded,  171 
Brakes,  259 

air  brake  rigging,  265,  267 

automatic  air,  269 

dimensions  of  brake  rigging,  265 

electric,  270 

equipment,  264 

friction  disc,  270 

hand  brake  rigging,  265,  267 

quick  action  automatic  air,  270 

shoes,  improper  method  of  hanging, 
264 

shoes,  proper  method  of  hanging,  263 

straight  air,  267 

track,  270 
Braking  (see  also  brakes),  64 

energy  required  for,  82 

forces  acting  during,  262 

friction  of  brake  shoes,  260 

motors  used  as  generators,  271 

reversal  of  motors,  271 

tests,  271 

Cars,  city,  226 

elevated  and  subway,  230 

frames,  220 

gasolene  electric,  300 

heating,  223 

lighting,  223 

motor  equipment,  221 


Cars,  number  and  capacity,  22 

pay-as-you-enter,  227 

suburban,  229 

trucks,  221 

weight,  48 

wiring,   226 
Car  demand  curves,  27 
Capacity  of  transmission  line,  14c 
Car  house,  design,  281 

equipment,  285 

fire  protection,  281 

floors,  283 

heating,  283 

lighting,  283 

location,  276 

offices,  and  employees'  quarters,  284 

pit  construction,  282 

repair  shops,  284 

tracks,  277 

transfer  table,  280 
Catenary  construction,  100,  loi 
Center  of  gravity  of  power  demands,  105 
Characteristics  of  motors,  35 

direct  current,  35,  39,  40 

single  phase,  240 
Charging  current  of  transmission  line, 

141 
Chimney,  164 

Coal  and  ash  handling  machinery,  165 
Coasting,  63 

energy  consumed  in,  83 
Competition,  relation  to  traffic  of  steam 

roads,  19,  21 
Condensers,  steam,  159 
Control,  alternating  current,  256 

combined  V  c.  d.  c,  257 

locomotive,  295 

master,  251 

multiple  unit,  252 

rheostatic,  246 

series  parallel,  246 

unit  switch,  252 

wiring,  a.  c.  d.  c.  Fig.  no 

wiring,  multiple  unit,  250 


333 


534 


INDEX. 


Control,  wiring,  series  parallel,  simpli- 
fied,   24S 

wiring,  unit  switch,  multiple  unit, 
Fig.  log 

wiring,  unit  switch,  simplified,  254 
Cost,  a.  c.  and  d.  c.  installation,  com- 
parative, 314,  315 

a.  c.  and  d.  c.  operation,  compara- 
tive, 315 

electrification,  330 

fuel  saved  by  electrification,  331 

power  station,  167,  168,  169 

power  station  maintenance  and 
operation,  150 

power  station  operation,  328 

roadbed,  218 

substation,  129,  130 

substation,  operation  and  main- 
tenance, 106,  107,  108,  329 

train  operation,  329 

transmission   system   maintenance, 

329 
Current  collection,  224 
Current-time  curves,  66,  67,  76 
Curves,  current-time,  66,  67,  76 

distance-time,  60,  66,  75 

kilo-volt-ampere-time,  69 

kilowatt-time,  69 

power-time,  68,  76 

resistance  due  to,  51,  52 

speed-time,  60,  75,  78,  79,  80 

substation  load,  89 

track,  measurement  of,  56 

Distance-time  curves,  60,  66,  75 
Distribution,  continuous  feeder,  92 

division  of  current  between  sub- 
stations, 94 

double  catenar}^,  loi 

feeder  with  infrequent  taps,  95 

high  voltage,  direct  current,  98 

Kelvin's  law,  99 

single-phase,  100 

third  rail,  103 

uniformly  loaded  feeders,  97 
Draft,  164 

Economy,  comparison  of  steam  engine 
and  turbine,  152 


Electrolysis,  178 

Engine,  steam,  economy,  152 

specifications,  154 
Energy  calculations,  81 

of  car,  81 

during  breaking  period,  82 

during  coasting,  83   • 

Feeders  with  infrequent  taps,  95 

Feed  water  heaters,  163 

Feed  water  pumps,  164 

Frequency,  effect  of  change  on  motors 

242 
Friction,  bearing  and  rolling,  49 
coefficient  for  brake  shoes,  260 

Gasoline  electric  car,  300 
Gear  ratio,  46 
Grades,  55 

Income,  gross,  21 

Induction  motor,  242 

Inertia  of  wheels  and  armature,  rotative, 


Kelvin's  Law,  99 
Kilo-volt-ampere-time  curves,  69 
Kilowatt-time  curves,  69 

Lightning  arrester,  electrolytic,  125 

Lightning  protection,  125 

Load  factor,  90 

Locomotives,  electric,   control  systems, 

295 
data,  298,  299 
New  York  Central,  289 
N.  Y.  N.  H.  &  H.,  290 
Pennsylvania,  296 
Locomotives,  steam  versus  electric,  3*25 

Motors,  adaptation  of  d.  c.  series  to  a.  c, 

234 
characteristics,  d.  c,  35,  39,  40 
characteristics  of  single-phase,  239 
commutating  pole,  233 
direct  current,  232 
frequency,  effect  of  change  on,  242 
induction,  242 
operation  of  single  phase  on  d.  c, 

240 


INDEX. 


I  T  c 
100 


Motors,  rating,  242 

repulsion,  241 

selection,  243 

single-phase,  234 

speed  curves,  37 

tests,  43 

torque  curves,  38 

torque,  determination  of,  42 

vector  diagram  of  single  phase,  235 
Motor  equipment,  221 
Motor  generator,  starting,  1 1 1 

versus  synchronous  converter,   no 

Offices  and  employees'  quarters,  284 

Paving,  214 

Pay-as-you-enter  cars,  227 
Population,  effect  upon  traffic,  13 

growth  of,  15 
Power  demand,  center  of  gravity  of,  105 
Power-station,  145 

arrangement  of  equipment,  166 

boilers,  162 

capacity,  149 

Chicago,     Lake    Shore    &     South 
Bend  Ry.,  14S 

chimney,  164 

coal  and  ash  handling  machinery, 
165 

condensers,  159 

cost,  167,  168,  169 

design,  147 

double  decked,  166 

draft,  164 

elevation  of,  151 

elevation  of  steam  turbine,  161 

exciters,  157 

feed  water  heaters,  163 

feed  water  pumps,  164 

fuel  saving   due   to   electrification, 

location,  145 

maintenance    and    operation    cost, 

150 
operation,  328 
plan  of  gas  engine,  158 
prime  movers,  149 
switchboard,  157 
transformers,  156 


Power-time  curves,  68,  76 

Rails,  210 

analysis,  212 

corrugation,  214 

joints,  174,  213 
Rail  joints,  213 

thermit,  174 

welded,  174 
Rating  of  motors,  242 
Reactance  of  transmission  line,  136 
Regulation,  transmission  line,   137 
Repair  shops,  284 
Repulsion  motor,  241 
Resistance,  air,  50 

due  to  curves,  51,  52 

formula  for  train,  51 

third  rail  and  track,  93 

train,  83 

transmission  Hne,  136 
Riding  habit,  18 
Right  of  way,  205 
Rolling  stock  (see  cars),  219 

Schedules,  train,  30 

Selection  of  motors,  243 

Signal  and  despatching  systems,  188 

automatic  block,  194 

block  signals  for  a.  c.  roads,  199 

cost,  block  signals,  201 

double  rail  a.  c.  signal,  200 

electric  railroad,  197 

lamp  signal,  191 

New  York  subway,  198 

single  rail  a.  c,  197 

steam  railroad,  196 

U.  S.  signal,  192 
Single-phase  motors,  234,  239,  240 
Speed-time  curves,  60,  75 

straight  line,  78 
Standardization  of  electrified  roads,  331 
Standing  by  preference,  28 
Steam  roads,  relation  of  competition  to 

traffic  of,  19,  21 
Storage  batter}-,  auxiliary,  121 
Substation,  arrangement  of  apparatus, 
122 

cost,  129,  130 

demand,  88 


32,^ 


INDEX. 


Substation,  design,  loq 

division  of  current  between,  94 

financial  considerations  of,  97 

high  voltage,  direct  current,  127 

lightning  protection,   125 

load  curve,  89 

location,  104 

operating  costs,  106,  107,  108 

operation  and  maintenance  cost,  3  29 

portable,  126 

single-phase,  12S 

switchboard,  117 

typical  elevation,  121,  122 

wiring,  123,  124 
Switchboard,  power  station,  157  , 

substation,  117 
Synchronous      converter,      comparative 
ratings,  115 

compounding,  117 

efficiency,  113 

starting,  iii 

versus  motor  generator,  no 

voltage  ratio,  114 

Tests,  braking,  271 

motor,  prony  brake,  271 

motor,  pumping  bacl^,  44 

motor  used  as  generator,  46 

rail  bonds,  175 
Thermit  rail  joints,  174 
Third  rail,  construction,  102 

distribution,  103 

resistance  of,  with  track,  93 

shoe,  225 
Ties,  20S 
Track,  ballast,  20S 

car  house,  277 

construction  in  Chicago,  185 

curves,  measurement  of,  56 

estimates,  218 

paving,  214 

rails,  210 

third  rail  and,  resistance  of,  93 

ties,  208,  209 

typical  construction,   207 
Traction,  electric,  growth  in  U.  S.,  11 
Traction,  electric  on  trunk  lines,  319 

alternating    versus    direct    current, 
305 


Traction,  electric  or  trunk  lines,  319 
cost,  314,  315,  326 
fuel  saving,  331 
locomotives,  325 

operating  cost  of  a.  c.  and  d.  c,  315 
power  station  operation,  328 
standardization,  331 
substation  operation   and   mainte- 
nance cost,  329 
train  operation  cost,  329 
transmission  system,  maintenance, 

329 
Tractive   effort,   consumed   in   rotating 

parts,  55 
Traffic,  effect  of  population  upon,  13 

of  steam  roads,  relation  of  competi- 
tion to,  20,  21 

statistics,  14 
Train  operating  costs,  329 
Train  schedules,  30 
Transformers,  112 

connections,  115,  116 

power  station,  156 

substation,  112 
Transmission  line,  131 

capacity,  140 

charging  current,  141 

electrical  calculations,  134 

maintenance,  329 

mechanical  strength,   133 

reactance,  136 

regulation,  137 

resistance,  136 

vector  diagram,  138,  139,  142 

voltage  determination,  137 
Trucks,  221 

Trunk  lines,  electric  traction  upon,  319 
Turbine,  steam,  economy,  152 

specifications,  153 

Welded  rail  joints,  174 

Wiring,  a.  c.  d.  c.  control,  Fig.  no 

car,   226 

multiple  unit,  250 

series  parallel,  simplified,  248 

substation,  123 

substation  diagram,  124 

unit  switch,  multiple  unit.  Fig.  109 

unit  switch,  simplified,  254 


^ 


2^ 


